On 27 December last year, astronomers using the ATLAS survey telescope in Chile discovered a small asteroid moving away from Earth. Follow up observations have revealed that the asteroid, 2024 YR4, is on a path that might lead to a collision with our planet on December 22 2032.

In other words, the newly-discovered space rock poses a significant impact threat to our planet.

It sounds like something from a bad Hollywood movie. But in reality, there’s no need to panic – this is just another day living on a target in a celestial shooting gallery.

So what’s the story? What do we know about 2024 YR4? And what would happen if it did collide with Earth?

A target in the celestial shooting gallery

As Earth moves around the Sun, it is continually encountering dust and debris that dates back to the birth of the Solar system. The system is littered with such debris, and the meteors and fireballs seen every night are evidence of just how polluted our local neighbourhood is.

But most of the debris is far too small to cause problems to life on Earth. There is far more tiny debris out there than larger chunks – so impacts from objects that could imperil life on Earth’s surface are much less frequent.

The most famous impact came some 66 million years ago. A giant rock from space, at least 10 kilometres in diameter, crashed into Earth – causing a mass extinction that wiped out something like 75% of all species on Earth.

Impacts that large are, fortunately, very rare events. Current estimates suggest that objects like the one which killed the dinosaurs only hit Earth every 50 million years or so. Smaller impacts, though, are more common.

On June 30 1908, there was a vast explosion in a sparsely populated part of Siberia. When explorers later reached the location of the explosion, they found an astonishing site: a forest levelled, with all the trees fallen in the same direction. As they moved around, the direction of the fallen trees changed – all pointing inwards towards the epicentre of the explosion.

In total, the Tunguska event levelled an area of almost 2,200 square kilometres – roughly equivalent to the area of greater Sydney. Fortunately, that forest was extremely remote. While plants and animals were killed in the blast zone, it is thought that, at most, only three people perished.

Estimates vary of how frequent such large collisions should be. Some argue that Earth should experience a similar impact, on average, once per century. Others suggest such collisions might only happen every 10,000 years or so. The truth is we don’t know – but that’s part of the fun of science.

More recently, a smaller impact created global excitement. On 15 February 2013, a small asteroid (likely about 18 metres in diameter) detonated near the Russian city of Chelyabinsk.

The explosion, about 30 kilometres above the Earth’s surface, generated a powerful shock-wave and extremely bright flash of light. Buildings were damaged, windows smashed, and almost 1,500 people were injured – although there were no fatalities.

It served as a reminder, however, that Earth will be hit again. It’s only a question of when.

Which brings us to our latest contender – asteroid 2024 YR4.

The 1-in-77 chance of collision to watch

2024 YR4 has been under close observation by astronomers for a little over a month. It was discovered just a few days after making a relatively close approach to our planet, and it is now receding into the dark depths of the Solar System. By April, it will be lost to even the world’s largest telescopes.

The observations carried out over the past month have allowed astronomers to extrapolate the asteroid’s motion forward over time, working out its orbit around the Sun. As a result, it has become clear that, on December 22 2032, it will pass very close to our planet – and may even collide with us.

At present, our best models of the asteroid’s motion have an uncertainty of around 100,000 kilometres in its position at the time it would be closest to Earth. At around 12,000 kilometres in diameter, our planet falls inside that region of uncertainty.

Calculations suggest there is currently around a 1-in-77 chance that the asteroid will crash into our planet at that time. Of course, that means there is still a 76-in-77 chance it will miss us.

When will we know for sure?

With every new observation of 2024 YR4, astronomers’ knowledge of its orbit improves slightly – which is why the collision likelihoods you might see quoted online keep changing. We’ll be able to follow the asteroid as it recedes from Earth for another couple of months, by which time we’ll have a better idea of exactly where it will be on that fateful day in December 2032.

But it is unlikely we’ll be able to say for sure whether we’re in the clear at that point.

Fortunately, the asteroid will make another close approach to the Earth in December 2028 – passing around 8 million kilometres from our planet. Astronomers will be ready to perform a wide raft of observations that will help us to understand the size and shape of the asteroid, as well as giving an incredibly accurate overview of where it will be in 2032.

At the end of that encounter, we will know for sure whether there will be a collision in 2032. And if there is to be a collision that year, we’ll be able to predict where on Earth that collision will be – likely to a precision of a few tens of kilometres.

How big would the impact be?

At the moment, we don’t know the exact size of 2024 YR4. Even through Earth’s largest telescopes, it is just a single tiny speck in the sky. So we have to estimate its size based on its brightness. Depending on how reflective the asteroid is, current estimates place it as being somewhere between 40 and 100 metres across.

What does that mean for a potential impact? Well, it would depend on exactly what the asteroid is made of.

The most likely scenario is that the asteroid is a rocky pile of rubble. If that turns out to be the case, then the impact would be very similar to the Tunguska event in 1908.

The asteroid would detonate in the atmosphere, with a shockwave blasting Earth’s surface as a result. The Tunguska impact was a “city killer” type event, levelling forest across a city-sized patch of land.

A less likely possibility is that the asteroid is made of metal. Based on its orbit around the Sun, this seems unlikely – but we can’t rule it out.

In that case, the asteroid would make it through the atmosphere intact, and crash into Earth’s surface. If it hit on the land, it would carve out a new impact crater, probably more than a kilometre across and a couple of hundred metres deep – something similar to Meteor Crater in Arizona.

Again, this would be quite spectacular for the region around the impact – but that would be about it.

Living in a remarkable time

This all sounds like doom and gloom. After all, we know that the Earth will be hit again – either by 2024 YR4 or something else. But there’s a real positive to take out of all this.

There has been life on Earth for more than 3 billion years. In all that time, impacts have come along and caused destruction and devastation many times.

But there has never been a species, to our knowledge, that understood the risk, could detect potential threats in advance, and even do something about the threat. Until now.

In just the past few years, we have discovered 11 asteroids before they hit our planet. In each case, we have predicted where they would hit, and watched the results.

We have also, in recent years, demonstrated a growing capacity to deflect potentially threatening asteroids. NASA’s DART mission (the Double Asteroid Redirection Test) was an astounding success.

For the first time in more than 3 billion years of life on Earth, we can do something about the risk posed by rocks from space. So don’t panic! But instead, sit back and watch the show.

Jonti Horner is a Professor of Astrophysics, University of Southern Queensland. This article is republished from The Conversation.

Using the largest gravitational wave detector ever made, we have confirmed earlier reports that the fabric of the universe is constantly vibrating. This background rumble is likely caused by collisions between the enormous black holes that reside in the hearts of galaxies.

The results from our detector – an array of rapidly spinning neutron stars spread across the galaxy – show this “gravitational wave background” may be louder than previously thought. We have also made the most detailed maps yet of gravitational waves across the sky, and found an intriguing “hot spot” of activity in the Southern Hemisphere.

Our research is published today in three papers in the Monthly Notices of the Royal Astronomical Society.

Ripples in space and time

Gravitational waves are ripples in the fabric of space and time. They are created when incredibly dense and massive objects orbit or collide with each other.

The densest and most massive objects in the universe are black holes, the remnants of dead stars. One of the only ways to study black holes is by searching for the gravitational waves they emit when they move near each other.

Just like light, gravitational waves are emitted in a spectrum. The most massive black holes emit the slowest and most powerful waves – but to study them, we need a detector the size of our galaxy.

The high-frequency gravitational waves created by collisions between relatively small black holes can be picked up with Earth-based detectors, and they were first observed in 2015. However, evidence for the existence of the slower, more powerful waves wasn’t found until last year.

Several groups of astronomers around the world have assembled galactic-scale gravitational wave detectors by closely observing the behaviour of groups of particular kinds of stars. Our experiment, the MeerKAT Pulsar Timing Array, is the largest of these galactic-scale detectors.

Today we have announced further evidence for low-frequency gravitational waves, but with some intriguing differences from earlier results. In just a third of the time of other experiments, we’ve found a signal that hints at a more active universe than anticipated.

We have also been able to map the cosmic architecture left behind by merging galaxies more accurately than ever before.

Black holes, galaxies and pulsars

At the centre of most galaxies, scientists believe, lives a gargantuan object known as a supermassive black hole. Despite their enormous mass – billions of times the mass of our Sun – these cosmic giants are difficult to study.

Astronomers have known about supermassive black holes for decades, but only directly observed one for the first time in 2019.

When two galaxies merge, the black holes at their centres begin to spiral towards each other. In this process they send out slow, powerful gravitational waves that give us an opportunity to study them.

We do this using another group of exotic cosmic objects: pulsars. These are extremely dense stars made mainly of neutrons, which may be around the size of a city but twice as heavy as the Sun.

Pulsars spin hundreds of times a second. As they rotate, they act like lighthouses, hitting Earth with pulses of radiation from thousands of light years away. For some pulsars, we can predict when that pulse should hit us to within nanoseconds.

Our gravitational wave detectors make use of this fact. If we observe many pulsars over the same period of time, and we’re wrong about when the pulses hit us in a very specific way, we know a gravitational wave is stretching or squeezing the space between the Earth and the pulsars.

However, instead of seeing just one wave, we expect to see a cosmic ocean full of waves criss-crossing in all directions – the echoing ripples of all the galactic mergers in the history of the universe. We call this the gravitational wave background.

A surprisingly loud signal – and an intriguing ‘hot spot’

To detect the gravitational wave background, we used the MeerKAT radio telescope in South Africa. MeerKAT is one of the most sensitive radio telescopes in the world.

As part of the MeerKAT Pulsar Timing Array, it has been observing a group of 83 pulsars for about five years, precisely measuring when their pulses arrive at Earth. This led us to find a pattern associated with a gravitational wave background, only it’s a bit different from what other experiments have found.

The pattern, which represents how space and time between Earth and the pulsars is changed by gravitational waves passing between them, is more powerful than expected.

This might mean there are more supermassive black holes orbiting each other than we thought. If so, this raises more questions – because our existing theories suggest there should be fewer supermassive black holes than we seem to be seeing.

The size of our detector, and the sensitivity of the MeerKAT telescope, means we can assess the background with extreme precision. This allowed us to create the most detailed maps of the gravitational wave background to date. Mapping the background in this way is essential for understanding the cosmic architecture of our universe.

It may even lead us to the ultimate source of the gravitational wave signals we observe. While we think it’s likely the background emerges from the interactions of these colossal black holes, it could also stem from changes in the early, energetic universe following the Big Bang – or perhaps even more exotic events.

The maps we’ve created show an intriguing “hot spot” of gravitational wave activity in the Southern Hemisphere sky. This kind of irregularity supports the idea of a background created by supermassive black holes rather than other alternatives.

However, creating a galactic-sized detector is incredibly complex, and it’s too early to say if this is genuine or a statistical anomaly.

To confirm our findings, we are working to combine our new data with results from other international collaborations under the banner of the International Pulsar Timing Array.

This article is republished from The Conversation under a Creative Commons license. Read the original article here.

(This article forms a part of the Science for All newsletter that takes the jargon out of science and puts the fun in! Subscribe now!)

Until now, scientists believed that there was no binary star system near Sagittarius A*, which is a supermassive black hole located at the centre of our Milky Way. However, new research suggests that one such system with the gravitationally bound stars is present in the S cluster, which is a group of high-velocity stars around Sagittarius A*. 

The findings were published in Nature Communications journal on Tuesday, December 17, 2024. 

Scientists have named this system D9 and it has similarities to G objects, which are strange celestial objects that “look like gas but behave like stars”. The study also predicts a lifespan of around three million years, before the stars merge into each other, because of their ongoing interaction with Sagittarius A*. 

The two stars in the D9 system complete an orbit in around 372 days. This orbit, given their sizes, is just stable enough so that the overwhelming gravity of the black hole does not tear them apart. They are also approximately 1.59 astronomical units (AU) apart, which is well below the tidal disruption radius of approximately 42.4 AU. Tidal disruption radius is the distance which allows a star to be torn away by the supermassive black hole, causing a tidal disruption event. 

The two stars in the D9 system are a Herbig Ae/Be star, and a T-Tauri star. 

The discovery suggests that even though this binary system was previously undetected, such stars can survive in S clusters in the vicinity of supermassive black holes for long periods of time – around a million years for Sagittarius A*. 

It is also important because the presence of a binary system alongside G objects allows us to partly resolve the “uncertain nature” of G objects. As the D9 system is predicted to merge, it may be possible that these G objects were binary systems that merged. 

From the Science pages

Question Corner

Flora and fauna

Chinese astronauts for the Shenzhou-18 mission, from right, Ye Guangfu, Li Cong, and Li Guangsu wave as they attend a send-off ceremony for their manned space mission at the Jiuquan Satellite Launch Center in northwestern China, April 25, 2024.
| Photo Credit: AP

Will the next human to walk on the Moon speak English or Mandarin? In all, 12 Americans landed on the lunar surface between 1969 and 1972. Now, both the US and China are preparing to send humans back there this decade.

However, the US lunar programme is delayed, in part because the spacesuits and lunar-landing vehicle are not ready. Meanwhile, China has pledged to put astronauts on the Moon by 2030 – and it has a habit of sticking to timelines.

Just a few years ago, such a scenario would have seemed unlikely. But there now appears to be a realistic possibility that China could beat the US in a race that America, arguably, has defined. So who will return there first, and does it really matter?

Nasa’s Moon programme is called Artemis. The US has involved international and commercial partners to spread the cost. Nasa set out a plan to get American boots back on lunar soil over the course of three missions. In November 2022, Nasa launched its Orion spacecraft on a loop around the Moon without humans aboard. This was the Artemis I mission.

Artemis II, scheduled for late 2025, is similar to Artemis I, but this time Orion will carry four astronauts. They will not land; this will be left for Artemis III. For this third mission, Nasa will send a man and the first woman to the lunar surface. Though as yet unnamed, one of them will be the first person of colour on the Moon.

Artemis III was scheduled to launch this year, but the timescale has slipped several times. A review in December 2023 gave a one in three chance that Artemis III would not have launched by February 2028. The mission is currently slated to happen no earlier than September 2026.

Meanwhile, China’s space programme seems to be moving at speed, without significant failures or delays. In April 2024, Chinese space officials announced that the country was on track to put its astronauts on the Moon by 2030.

It’s an extraordinary trajectory for a country that launched its first astronaut in 2003. China has been operating space stations since 2011 and has been ticking off important, challenging firsts through its Chang’e lunar exploration programme.

These robotic missions returned samples from the surface, including from the lunar far side. They have tested technology that could be crucial for landing humans. The next mission will touch down at the lunar south pole, a region that attracts intense interest because of the presence of water ice in shadowed craters there.

This water could be used for life support by a lunar base and turned into rocket propellant. Making rocket propellant on the Moon would be cheaper than bringing it from Earth, making lunar exploration more affordable. It is for these reasons that Artemis III will land at the south pole. It’s also the planned location for US and Chinese-led bases.

On September 28 2024, China showed off a spacesuit, to be worn by its Moon walkers, or “selenauts”. The suit is designed to protect the wearer against extreme temperature variations and unfiltered solar radiation. It is lightweight and flexible. Is it a sign of China already overtaking the US in one aspect of the Moon race? The company manufacturing the Artemis Moon suit, Axiom Space, is currently having to modify several aspects of the reference design given to them by Nasa.

The lander that will carry US astronauts from lunar orbit to the surface is also delayed. In 2021, Elon Musk’s SpaceX was given the contract to build this vehicle. It is based on SpaceX’s Starship, which consists of a 50m-long spacecraft that launches on the most powerful rocket ever built.

On October 13 2024, Starship scored a successful fifth test flight. But several challenging steps are required before the Starship Human Landing System can carry astronauts down to the lunar surface. Starship cannot fly directly to the Moon. It must refuel in Earth orbit first (using other Starships that act as propellant “tankers”). SpaceX needs to demonstrate refuelling and conduct a test landing on the Moon without crew before Artemis III can proceed.

In addition, during Artemis I, Orion’s heat shield suffered considerable damage as the spacecraft made the high-temperature return through Earth’s atmosphere. Nasa engineers have been working to find a remedy before the Artemis II mission.

Too complicated?

Some critics argue that Artemis is too complex, referring to the intricate way in which astronauts and Moon lander are brought together in lunar orbit, the large number of independently operating commercial partners and the number of Starship launches required. Depending who you ask, between four and 15 Starship flights are needed to complete the refuelling for Artemis III.

Former Nasa administrator Michael Griffin has advocated a simpler strategy, broadly along the lines of how China expects to accomplish its lunar landing. His vision sees Nasa relying on traditional commercial partners such as Boeing, rather than relative “newbies” such as SpaceX.

However, simple is not necessarily better or cheaper. The Apollo programme was simpler, but at almost three times the cost of Artemis. SpaceX has been more successful, and economical, than Boeing in sending crews to the International Space Station.

New technology is not developed through simple, tried approaches but in bold endeavours that push boundaries. The James Webb Space Telescope is highly complex, with its folded mirror and distant position in space, but it allows astronomers to peer into the depths of the universe as no other telescope can. Innovation is especially crucial bearing in mind future ambitions such as asteroid mining and a settlement on Mars.

Does it matter whether the first 21st-century selenauts are Chinese or American? This is largely a question about the relationship between governments and their citizens, and between nations.

Democratic governments depend on public support to safeguard funding for expensive, long-term ventures – and prestige is an important selling point. But prestige in a 21st-century Moon race will be earned by doing it well, not sooner. Rushing back to the Moon could be costly, both financially and in the risk to human life.

Governments must set an example of responsible behaviour. Peace, inclusivity and sustainability should be guiding principles. Going back to the Moon must not be about dominion or superiority. It should be a chance to show that we can improve on how we have previously behaved on Earth.

This article is republished from The Conversation under a Creative Commons license. Read the original article here.

This artist’s illustration shows the wayward interstellar visitor ‘Oumuamua (pronounced oh-MOO-ah-MOO-ah) racing toward the outskirts of our solar system. The object, heated by the Sun (lower right),
is venting gaseous material from its surface, as a comet would.
| Photo Credit: Reuters

In 2017, NASA discovered and later confirmed the first interstellar object to enter our Solar System.

It wasn’t aliens. But artist impressions of the object (called ‘Oumuamua, the Hawaiian word for “scout”) do resemble an alien spaceship out of a sci-fi novel. This strange depiction is because astronomers don’t quite know how to classify the interstellar visitor.

Its speed and path around the Sun don’t match a typical asteroid, but it also has no bright tail or nucleus (icy core) we normally associate with comets. However, ‘Oumuamua has erratic motions that are consistent with gas escaping from its surface. This “dark comet” has had astronomers scratching their heads ever since.

Flash forward to today, and more of these mysterious objects have been discovered, with another ten announced just last week. While their nature and origins remain elusive, astronomers recently confirmed dark comets fall into two main categories: smaller objects that reside in our inner Solar System, and larger objects (100 metres or more) that remain beyond the orbit of Jupiter.

In fact, 3200 Phaethon – the parent body of the famous Geminid meteor shower – may be one of these objects.

How do dark comets differ from normal comets?

Comets, often described as the Solar System’s “dirty snowballs”, are icy bodies made of rock, dust and ices. These relics of the early Solar System are critical to unlocking key mysteries around our planet’s formation, the origins of Earth’s water, and even the ingredients for life.

Astronomers are able to study comets as they make their close approach to our Sun. Their brilliant tails form as sunlight vaporises their icy surfaces. But not all comets put on such a dazzling display.

The newly discovered dark comets challenge our typical understanding of these celestial wanderers.

Dark comets are more elusive than their bright siblings. They lack the glowing tails and instead resemble asteroids, appearing as a faint point of light against the vast darkness of space.

However, their orbits set them apart. Like bright comets, dark comets follow elongated, elliptical paths that bring them close to the Sun before sweeping back out to the farthest reaches of the Solar System.

They go beyond Pluto, some even making it out to the Oort Cloud, a vast bubble of tiny objects at the fringe of our Solar System. Their speed and paths are what allow astronomers to determine their origins.

But what makes these comets so dark? There are three main reasons: size, spin and composition or age.

Dark comets are often small, just a few metres to a few hundred metres wide. This leaves less surface area for material to escape and form into the beautiful tails we see on typical comets. They often spin quite rapidly and disperse escaping gas and dust in all directions, making them less visible.

Lastly, their composition and age may result in weaker or no gas loss, as the materials that go into the tails of bright comets are depleted over time.

These hidden travellers may be just as important for astronomical studies, and they may even be related to their bright counterparts. Now, the challenge is to find more dark comets.

How can we find dark comets?

How do we even find these mysterious dark comets in the first place? As they get closer to the Sun, we don’t see spectacular tails of debris.

Instead, we rely on the light they reflect from our Sun.

These little guys might be stealthy for our eyes, but they are often no match for our large telescopes around the world. The discovery of ten new dark comets revealed last week was all thanks to one amazing instrument, the Dark Energy Camera (DECam) on a large telescope in Chile.

This camera can’t “see” dark energy directly, but it was designed to take massive photos of our universe – for us to see distant stars, galaxies and even hidden Solar System objects.

In their recent study, astronomers pieced together that some of these nightly images contained likely dark comets.

The good news is, we are starting to focus more attention on these objects and on how to find them.

In even better news, in 2025, we’ll have a brand new mega camera in Chile ready to find them. This will be the Vera C. Rubin Observatory, with the largest digital camera ever built.

It will allow us to take more images of our night sky more quickly, and see objects that are even fainter. It’s likely that in the next ten years we could double or even triple the amount of known dark comets, and start to understand their interesting origin stories.

There could be more ‘Oumuamua-like objects out there, just waiting for us to find them.

This article is republished from The Conversation under a Creative Commons license. Read the original article here.

Spiral galaxy NGC 628, located 32 million light-years away from Earth, is seen in an undated image from the James Webb Space Telescope.
| Photo Credit: Reuters

Fresh corroboration of the perplexing observation that the universe is expanding more rapidly than expected has scientists pondering the cause – perhaps some unknown factor involving the mysterious cosmic components dark energy and dark matter.

Two years of data from NASA’s James Webb Space Telescope have now validated the Hubble Space Telescope’s earlier finding that the rate of the universe’s expansion is faster – by about 8% – than would be expected based on what astrophysicists know of the initial conditions in the cosmos and its evolution over billions of years. The discrepancy is called the Hubble Tension.

The observations by Webb, the most capable space telescope ever deployed, appear to rule out the notion that the data from its forerunner Hubble was somehow flawed due to instrument error.

“This is the largest sample of Webb Telescope data – its first two years in space – and it confirms the puzzling finding from the Hubble Space Telescope that we have been wrestling with for a decade – the universe is now expanding faster than our best theories can explain,” said astrophysicist Adam Riess of Johns Hopkins University in Maryland, lead author of the study published on Monday (December 9, 2024) in the Astrophysical Journal.

“Yes, it appears there is something missing in our understanding of the universe,” added Riess, a 2011 Nobel laureate in physics for the co-discovery of the universe’s accelerating expansion. “Our understanding of the universe contains a lot of ignorance about two elements – dark matter and dark energy – and these make up 96% of the universe, so this is no small matter.”

“The Webb results can be interpreted to suggest there may be a need to revise our model of the universe, although it is very difficult to pinpoint what this is at the moment,” said Siyang Li, a Johns Hopkins doctoral student in astronomy and astrophysics and a study co-author.

Dark matter, thought to comprise about 27% of the universe, is a hypothesised form of matter that is invisible but is inferred to exist based on its gravitational effects on ordinary matter – stars, planets, moons, all the stuff on Earth – which accounts for roughly 5% of the universe.

Dark energy, believed to comprise approximately 69% of the universe, is a hypothesised form of energy permeating vast swathes of space that counteracts gravity and drives the universe’s accelerating expansion.

What might explain the anomalous expansion rate?

“There are many hypotheses that involve dark matter, dark energy, dark radiation – for example, neutrinos (a type of ghostly subatomic particle) – or gravity itself having some exotic properties as possible explanations,” Riess said.

The researchers employed three different methods to measure a specific telltale metric – distances from Earth to galaxies where a type of pulsating star called Cepheids have been documented. The Webb and Hubble measurements were in harmony.

The universe’s expansion rate, a figure called the Hubble constant, is measured in kilometers per second per megaparsec, a distance equal to 3.26 million light-years. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

Under the standard model of cosmology – basically, the conventional wisdom concerning the universe – the value of the Hubble constant should be about 67-68. The Hubble and Webb data give a value averaging about 73, with a range of about 70-76.

The Big Bang event 13-14 billion years ago initiated the universe, and it has been expanding ever since. Scientists in 1998 disclosed that this expansion was actually accelerating, with dark energy as the hypothesized reason.

The new study looked at Webb data covering about a third of Hubble’s full slate of relevant galaxies. The researchers in 2023 announced that earlier interim Webb data validated the Hubble findings.

So how might this Hubble Tension mystery be solved?

“We need more data to better characterize this clue. Exactly what size is it (the discrepancy)? Is the mismatch at the lower end – 4-5% – or the higher end – 10-12% – of what the current data allows? Over what range of cosmic time is it present? These will further inform ideas,” Riess said.

Water is ubiquitous on Earth – about 70% of Earth’s surface is covered by the stuff. Water is in the air, on the surface and inside rocks. Geologic evidence suggests water has been stable on Earth since about 4.3 billion years ago.

The history of water on early Mars is less certain. Determining when water first appeared, where and for how long, are all burning questions that drive Mars exploration. If Mars was once habitable, some amount of water was required.

We studied the mineral zircon in a meteorite from Mars and found evidence that water was present when the zircon crystal formed 4.45 billion years ago. Our results, published in the journal Science Advances today, may represent the oldest evidence for water on Mars.

A wet red planet

Water has long been recognised to have played an important role in early Martian history. To place our results in a broader context, let’s first consider what “early Mars” means in terms of the Martian geological timescale, and then consider the different ways to look for water on Mars.

Like Earth, Mars formed about 4.5 billion years ago. The history of Mars has four geological periods. These are the Amazonian (from today back to 3 billion years), the Hesperian (3 billion to 3.7 billion years ago), the Noachian (3.7 billion to 4.1 billion years ago) and the Pre-Noachian (4.1 billion to about 4.5 billion years ago).

Evidence for water on Mars was first reported in the 1970s when NASA’s Mariner 9 spacecraft captured images of river valleys on the Martian surface. Later orbital missions, including Mars Global Surveyor and Mars Express, detected the widespread presence of hydrated clay minerals on the surface. These would have needed water.

The Martian river valleys and clay minerals are mainly found in Noachian terrains, which cover about 45% of Mars. In addition, orbiters also found large flood channels – called outflow channels – in Hesperian terrains. These suggest the short-lived presence of water on the surface, perhaps from groundwater release.

Most reports of water on Mars are in materials or terrains older than 3 billion years. More recent than that, there isn’t much evidence for stable liquid water on Mars.

But what about during the Pre-Noachian? When did water first show up on Mars?

A window to Pre-Noachian Mars

There are three ways to hunt for water on Mars. The first is using observations of the surface made by orbiting spacecraft. The second is using ground-based observations such as those taken by Mars rovers.

The third way is to study Martian meteorites that have landed on Earth, which is what we did.

In fact, the only Pre-Noachian material we have available to study directly is found in meteorites from Mars. A small number of all meteorites that have landed on Earth have come from our neighbouring planet.

An even smaller subset of those meteorites, believed to have been ejected from Mars during a single asteroid impact, contain Pre-Noachian material.

The “poster child” of this group is an extraordinary rock called NWA7034, or Black Beauty.

Black Beauty is a famous Martian meteorite made up of broken-up surface material, or regolith. In addition to rock fragments, it contains zircons that formed from 4.48 billion to 4.43 billion years ago. These are the oldest pieces of Mars known.

While studying trace elements in one of these ancient zircons we found evidence of hydrothermal processes – meaning they were exposed to hot water when they formed in the distant past.

Trace elements, water and a connection to ore deposits

The zircon we studied is 4.45 billion years old. Within it, iron, aluminium and sodium are preserved in abundance patterns like concentric layers, similar to an onion.

This pattern, called oscillatory zoning, indicates that incorporation of these elements into the zircon occurred during its igneous history, in magma.

The problem is that iron, aluminium and sodium aren’t normally found in crystalline igneous zircon – so how did these elements end up in the Martian zircon?

The answer is hot water.

In Earth rocks, finding zircon with growth zoning patterns for elements like iron, aluminium and sodium is rare. One of the only places where it has been described is from Olympic Dam in South Australia, a giant copper, uranium and gold deposit.

The metals in places like Olympic Dam were concentrated by hydrothermal (hot water) systems moving through rocks during magmatism.

Hydrothermal systems form anywhere that hot water, heated by volcanic plumbing systems, moves through rocks. Spectacular geysers at places like Yellowstone National Park in the United States form when hydrothermal water erupts at Earth’s surface.

Finding a hydrothermal Martian zircon raises the intriguing possibility of ore deposits forming on early Mars.

Previous studies have proposed a wet Pre-Noachian Mars. Unusual oxygen isotope ratios in a 4.43 billion-year-old Martian zircon were previously interpreted as evidence for an early hydrosphere. It has even been suggested that Mars may have had an early global ocean 4.45 billion years ago.

The big picture from our study is that magmatic hydrothermal systems were active during the early formation of Mars’ crust 4.45 billion years ago.

It’s not clear whether this means surface water was stable at this time, but we think it’s possible. What is clear is that the crust of Mars, like Earth, had water shortly after it formed – a necessary ingredient for habitability.

This article is republished from The Conversation under a Creative Commons license. Read the original article here.

A team led by researchers at MIT in the United States has discovered large molecules containing carbon in a distant interstellar cloud of gas and dust.
| Photo Credit: Space Telescope Science Institute Office of Public Outreach

A team led by researchers at MIT in the United States has discovered large molecules containing carbon in a distant interstellar cloud of gas and dust.

This is exciting for those of us who keep lists of known interstellar molecules in the hope that we might work out how life arose in the universe.

But it’s more than just another molecule for the collection. The result, reported today in the journal Science, shows that complex organic molecules (with carbon and hydrogen) likely existed in the cold, dark gas cloud that gave rise to our Solar System.

Furthermore, the molecules held together until after the formation of Earth. This is important for our understanding of the early origins of life on our planet.

Difficult to destroy, hard to detect

The molecule in question is called pyrene, a polycyclic aromatic hydrocarbon or PAH for short. The complicated-sounding name tells us these molecules are made of rings of carbon atoms.

Carbon chemistry is the backbone of life on Earth. PAHs have long been known to be abundant in the interstellar medium, so they feature prominently in theories of how carbon-based life on Earth came to be.

We know there are many large PAHs in space because astrophysicists have detected signs of them in visible and infrared light. But we didn’t know which PAHs they might be in particular.

Pyrene is now the largest PAH detected in space, although it’s what is known as a “small” or simple PAH, with 26 atoms. It was long thought such molecules could not survive the harsh environment of star formation when everything is bathed in radiation from the newborn suns, destroying complex molecules.

In fact, it was once thought molecules of more than two atoms could not exist in space for this reason, until they were actually found. Also, chemical models show pyrene is very difficult to destroy once formed.

Last year, scientists reported they found large amounts of pyrene in samples from the asteroid Ryugu in our own Solar System. They argued at least some of it must have come from the cold interstellar cloud that predated our Solar System.

So why not look at another cold interstellar cloud to find some? The problem for astrophysicists is that we don’t have the tools to detect pyrene directly – it’s invisible to radio telescopes.

Using a tracer

The molecule the team has detected is called 1-cyanopyrene, what we call a “tracer” for pyrene. It is formed from pyrene interacting with cyanide, which is common in interstellar space.

The researchers used the Green Bank Telescope in West Virginia to look at the Taurus molecular cloud or TMC-1, in the Taurus constellation. Unlike pyrene itself, 1-cyanopyrene can be detected by radio telescopes. This is because 1-cyanopyrene molecules act as small radio-wave emitters – tiny versions of earthly radio stations.

As scientists know the proportions of 1-cyanopyrene compared to pyrene, they can then estimate the amount of pyrene in the interstellar cloud.

The amount of pyrene they found was significant. Importantly, this discovery in the Taurus molecular cloud suggests a lot of pyrene exists in the cold, dark molecular clouds that go on to form stars and solar systems.

The complex birth of life

We are gradually building a picture of how life on Earth evolved. This picture tells us that life came from space – well, at least the complex organic, pre-biological molecules needed to form life did.

That pyrene survives the harsh conditions associated with the birth of stars, as shown by the findings from Ryugu, is an important part of this story.

Simple life – consisting of a single cell – appeared in Earth’s fossil record almost immediately (in geological and astronomical terms) after the planet’s surface had cooled enough to not vaporise complex molecules. This happened more than 3.7 billion years ago in Earth’s approximately 4.5 billion history.

For simple organisms to then appear so quickly in the fossil record, there’s just not enough time for chemistry to start with mere simple molecules of two or three atoms.

The new discovery of 1-cyanopyrene in the Taurus molecular cloud shows complex molecules could indeed survive the harsh conditions of our Solar System’s formation. As a result, pyrene was available to form the backbone of carbon-based life when it emerged on the early Earth some 3.7 billion years ago.

This discovery also links to another important finding of the last decade – the first chiral molecule in the interstellar medium, propylene oxide. We need chiral molecules to make the evolution of simple lifeforms work on the surface of the early Earth.

So far, our theories that molecules for early life on Earth came from space are looking good.

This article is republished from The Conversation under a Creative Commons license. Read the original article here.

Reporters gather around a piece of a meteorite, which according to local authorities and scientists was lifted from the bottom of the Chebarkul Lake, placed on display in a local museum in Chelyabinsk, October 18, 2013. Each year, roughly 17,000 of these fireballs not only enter Earth’s atmosphere, but survive the perilous journey to the surface.
| Photo Credit: Reuters

The sight of a fireball streaking across the sky brings wonder and excitement to children and adults alike. It’s a reminder that Earth is part of a much larger and incredibly dynamic system.

Each year, roughly 17,000 of these fireballs not only enter Earth’s atmosphere, but survive the perilous journey to the surface. This gives scientists a valuable chance to study these rocky visitors from outer space.

Scientists know that while some of these meteorites come from the Moon and Mars, the majority come from asteroids. But two separate studies published in Nature today have gone a step further. The research was led by Miroslav Brož from Charles University in the Czech Republic, and Michaël Marsset from the European Southern Observatory in Chile.

The papers trace the origin of most meteorites to just a handful of asteroid breakup events – and possibly even individual asteroids. In turn, they build our understanding of the events that shaped the history of the Earth – and the entire solar system.

What is a meteorite?

Only when a fireball reaches Earth’s surface is it called a meteorite. They are commonly designated as three types: stony meteorites, iron meteorites, and stony-iron meteorites.

Stony meteorites come in two types.

Also Read | Ancient meteorite was ‘giant fertilizer bomb’ for life on Earth

The most common are the chondrites, which have round objects inside that appear to have formed as melt droplets. These comprise 85% of all meteorites found on Earth.

Most are known as “ordinary chondrites”. They are then divided into three broad classes – H, L and LL – based on the iron content of the meteorites and the distribution of iron and magnesium in the major minerals olivine and pyroxene. These silicate minerals are the mineral building blocks of our Solar System and are common on Earth, being present in basalt.

“Carbonaceous chondrites” are a distinct group. They contain high amounts of water in clay minerals, and organic materials such as amino acids. Chondrites have never been melted and are direct samples of the dust that originally formed the solar system.

The less common of the two types of stony meteorites are the so-called “achondrites”. These do not have the distinctive round particles of chondrites, because they experienced melting on planetary bodies.

The asteroid belt

Asteroids are the primary sources of meteorites.

Most asteroids reside in a dense belt between Mars and Jupiter. The asteroid belt itself consists of millions of asteroids swept around and marshalled by the gravitational force of Jupiter.

The interactions with Jupiter can perturb asteroid orbits and cause collisions. This results in debris, which can aggregate into rubble pile asteroids. These then take on lives of their own.

It is asteroids of this type which the recent Hayabusa and Osiris-REx missions visited and returned samples from. These missions established the connection between distinct asteroid types and the meteorites that fall to Earth.

S-class asteroids (akin to stony meteorites) are found on the inner regions of the belt, while C-class carbonaceous asteroids (akin to carbonaceous chondrites) are more commonly found in the outer regions of the belt.

But, as the two Nature studies show, we can relate a specific meteorite type to its specific source asteroid in the main belt.

One family of asteroids

The two new studies place the sources of ordinary chondrite types into specific asteroid families – and most likely specific asteroids. This work requires painstaking back-tracking of meteoroid trajectories, observations of individual asteroids, and detailed modelling of the orbital evolution of parent bodies.

The study led by Miroslav Brož reports that ordinary chondrites originate from collisions between asteroids larger than 30 kilometres in diameter that occurred less than 30 million years ago.

The Koronis and Massalia asteroid families provide appropriate body sizes and are in a position that leads to material falling to Earth, based on detailed computer modelling. Of these families, asteroids Koronis and Karin are likely the dominant sources of H chondrites. Massalia (L) and Flora (LL) families are by far the main sources of L- and LL-like meteorites.

Also Read | Asteroid that doomed the dinosaurs originated beyond Jupiter

The study led by Michaël Marsset further documents the origin of L chondrite meteorites from Massalia.

It compiled spectroscopic data – that is, characteristic light intensities which can be fingerprints of different molecules – of asteroids in the belt between Mars and Jupiter. This showed that the composition of L chondrite meteorites on Earth is very similar to that of the Massalia family of asteroids.

The scientists then used computer modelling to show an asteroid collision that occurred roughly 470 million years ago formed the Massalia family. Serendipitously, this collision also resulted in abundant fossil meteorites in Ordovician limestones in Sweden.

In determining the source asteroid body, these reports provide the foundations for missions to visit the asteroids responsible for the most common outerspace visitors to Earth. In understanding these source asteroids, we can view the events that shaped our planetary system.

Trevor Ireland receives funding from the Australian Research Council for research into the samples returned by the Hayabusa and Osiris-REx missions. He is a past President of the Meteoritical Society, the international organisation responsible for classification and cataloguing meteorites.This article is republished from The Conversation.

A view of Jupiter’s moon Europa created from images taken by NASA’s Galileo spacecraft in the late 1990’s, according to NASA, obtained by Reuters May 14, 2018.
| Photo Credit: Reuters

On October 10, NASA is launching a hotly anticipated new mission to Jupiter’s fourth-largest moon, Europa.

Called Europa Clipper, the spacecraft will conduct a detailed study of the moon, looking for potential places where Europa might host alien life.

It’s the largest planetary exploration spacecraft NASA has ever made: as wide as a basketball court when its solar sails are unfolded. It has a mass of about 6,000 kilograms – the weight of a large African elephant.

But why are we sending a hulking spacecraft all the way to Europa?

Looking for life away from Earth

The search for life in places other than Earth usually focuses on our neighbour Mars, a planet that’s technically in the “habitable zone” of our Solar System. But Mars is not an attractive place to live, due to its lack of atmosphere and high levels of radiation. However, it’s close to Earth, making it relatively easy to send missions to explore it.

But there are other places in the Solar System that could support life – some of the moons of Jupiter and Saturn. Why? They have liquid water.

Here on Earth, water is the solvent of life: water dissolves salts and sugars, and facilitates the chemical reactions needed for life on Earth to proceed. It’s possible life forms exist elsewhere that rely on liquid methane or carbon dioxide or something else, but life as we know it uses water.

The reason there’s liquid water so far out in the Solar System is because Jupiter and Saturn, the gas giants, wield immense gravitational power over their moons.

Saturn’s moons, Titan and Enceladus, are stretched and compressed by gravity as they go around their host planet. This movement results in vast underground oceans with a surface of solid ice, with plumes of water vapour exploding 9,600 kilometres from the surface.

It is strongly suspected that Europa is the same. While we know a lot about Europa from more than four centuries of observation, we have not confirmed it has an under-ice liquid ocean like Titan and Enceladus.

But all clues point to yes. Europa has a smooth surface despite being hit by many meteors, suggesting the surface is young, recently replaced. Ice volcanoes raining down water over the surface would make sense.

It also has a magnetic field, suggesting that like Earth, Europa has a liquid layer inside (on Earth, this liquid is molten rock).

What will Europa Clipper do?

At the surface, Europa is bombarded by high levels of space radiation, concentrated by Jupiter. But deeper down, the thick ice sheet could be protecting life in the liquid subsurface ocean.

This means it would be difficult for us to find concrete evidence for life without drilling down deep. But where to look? Through flybys of the icy moon, Europa Clipper will be looking at areas where life could be dwelling under the icy shell.

To achieve this, Europa Clipper has nine scientific instruments. These include a wide-angle camera to study geologic activity and a thermal imaging system to measure surface texture and detect warmer regions on the surface.

There’s also a spectrometer for looking at the chemical composition of the gases and surface of Europa, and for any explosive plumes of water from the surface. The mission also has tools for mapping the moon’s surface.

Other instruments will measure the depth and salt levels of the moon’s ocean and the thickness of its ice shell, and also how Europa flexes within the strong gravitational pull of Jupiter.

Excitingly, a mass spectrometer will analyse the gases of the moon’s faint atmosphere and potential plumes of water. By examining the material ejected from the plumes, we can understand what is hidden within the under-ice oceans of Europa.

A dust analyser will also look at matter that has been ejected from Europa’s surface by tiny meteorites or released from the plumes.

Unfortunately, we will have to wait a while for any discoveries. Europa Clipper will take more than five years to reach Jupiter. And the mission is only equipped to look for the potential of life, not life itself. If we see evidence that might point towards life, we will need future missions to return and explore Europa in depth.

So we must be patient. But this is an exciting opportunity for humanity to get one step closer to find life beyond our own home planet.

This article is republished from The Conversation under a Creative Commons license. Read the original article.