Tag: Solar System

Where Did Mars’s Moons Come From?

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Where did the moons of Mars come from? That’s a question scientists still can’t answer. We know that Earth’s moon was likely formed from a giant impact on our planet about 4.5 billion years ago. Some moons in the solar system, such as several of Jupiter’s smaller satellites, appear to be captured asteroids. It remains unclear which of these two formation routes holds true for Mars’s moons, Phobos and Deimos—but we may soon have an answer. A Japanese spacecraft launching next year will attempt to bring samples back from Phobos. The mission will build on exciting new results from a United Arab Emirates (U.A.E.) orbiter at Mars that suggest a planetary origin for the two moons. “There’s room to be surprised, but I think we’re going to figure it out,” says Jemma Davidson of Arizona State University.

On April 24 the U.A.E. announced that its orbiter, Hope, had studied the smaller of Mars’s two moons, Deimos. The spacecraft returned some of the best data and images of Deimos yet from as low as 100 kilometers above the moon’s surface. Those results suggest the Deimos’s composition more closely matches Mars than that of a class of asteroids that was previously flagged as the likely raw material for Deimos and Phobos alike: D-type asteroids in the outer asteroid belt between Mars and Jupiter. “We don’t believe that [Deimos] is an asteroid,” says Hessa Al Matroushi, science lead of the mission at the Mohammed Bin Rashid Space Center in Dubai.

To find out for sure, scientists want to return samples of Phobos to Earth. An attempt by Russia to do so ended in failure in 2012, when its Phobos-Grunt spacecraft crashed into the Pacific Ocean shortly after launch. “It never got out of Earth orbit,” says John Logsdon, a space historian and professor emeritus at George Washington University’s Space Policy Institute. The Japan Aerospace Exploration Agency (JAXA) is hoping to avoid the same fate with its Martian Moons eXploration (MMX) mission. The solar-powered spacecraft, expected to launch in September 2024, weighs in at more than three metric tons and is roughly the size of an SUV. It will aim to enter Martian orbit in August 2025 before sidling up to Phobos in 2026 to scoop samples and return them to Earth by 2029. The mission is “super complex” but should be highly rewarding, says Patrick Michel of the Côte d’Azur Observatory in France, a European collaborator on MMX and a member of the mission’s science board.

On April 17 NASA and JAXA announced they would be partnering on the mission. As part of the partnership, NASA selected 10 U.S. scientists to work on MMX and will also supply two instruments for the spacecraft. “We’ve got great partners at JAXA, and they are leading this ambitious mission to bring back the first samples of the Martian moon Phobos,” said Bill Nelson, NASA’s administrator, in a video message posted to Twitter. “Together, we’re going to deepen our knowledge of the solar system.”

Of Mars’s two moons, Phobos is slightly larger. Both are irregularly shaped, like potatoes. Phobos is about 27 km across on its longest side, and Deimos is 15 km across. Phobos is also the closer of the two to Mars. It orbits just 6,000 km above the surface and completes an orbit every seven hours and 39 minutes. Deimos, at more than 23,000 km in altitude, takes slightly more than 30 hours to orbit. Both moons have been imaged by several spacecraft before, most notably by NASA’s Viking 2 orbiter in 1977 and by the Mars Reconnaissance Orbiter in the 2000s and even by the Curiosity rover from the surface of Mars in 2013. But no spacecraft has ever landed on either moon.

Japan’s MMX mission will attempt to change that. It builds on the success of the nation’s asteroid sampling missions, Hayabusa and Hayabusa2, which returned samples of asteroids in 2010 and 2020, respectively. Both of those, however, spent mere seconds brushing across the surfaces of their targets. MMX will land on Phobos in two locations and spend two hours on the surface collecting about 10 grams of material in total. “That’s a big difference with Hayabusa,” Michel says. Surface operations on Phobos pose many challenges because the moon has just a thousandth of Earth’s gravity—and an uneven gravity field at that, given its unusual shape. MMX will gather samples using two methods: a coring sampler on an extendable arm to collect specimens from deeper than two centimeters and a pneumatic sampler to kick up material from the surface.

Before MMX collects its samples, however, it will seek to ensure a smaller landing takes place. In 2026 or 2027 the spacecraft will deploy a small rover on the surface, developed by scientists in France and Germany. The rover, the size of a microwave, will be dropped from a height of 45 meters when the spacecraft performs a practice landing attempt. After tumbling on the surface, the rover will then be righted by its four extendable wheels to begin a 100-day mission. The moon’s weak, irregular gravitational pull means that the rover, despite weighing just 25 kilograms, will not be able to travel faster than a snail’s pace because it would otherwise risk launching itself into space.

“If we’re going quicker than 80 millimeters per second, we might flip over the rover or even leave the Phobos system,” says Markus Grebenstein of the German Aerospace Center, the project manager for the rover. Accounting for the rover’s limited lifetime, that speed limit “basically restricts our range to about 100 meters.” Even so, the rover should prove invaluable. It will study the surface of Phobos and give the main MMX spacecraft vital information on the moon’s surface properties that will be incorporated into the two landing attempts. The rover will also test robotic operations on a small body such as Phobos. A stretch goal might be to push the rover to its limits by spinning up its back wheels at the end of the mission in an attempt to flip it. “The rover would easily be able to do a backflip,” Grebenstein says. “We might be allowed to do experiments like that at end of its life.”

The target for MMX will be sampling “the most pristine material on Phobos,” Michel says, which may include hints to its origin. The samples may have a hidden bonus, too. The surface of Phobos is thought to be covered in some material that was ejected from Mars via impacts and then settled on the moon. So when Japan brings its samples to Earth in 2029, they may well contain the first pristine ones collected from the planet itself, beating NASA’s multi-billion-dollar Mars Sample Return effort, which is not expected to send samples back to our planet until 2033 at the earliest, by a considerable margin. MMX’s samples are unlikely to contain any evidence of past life or habitability on Mars, but they may provide useful information about its past geology. “We hope we can capture them in the sampling mechanism,” Michel says. “We could have the first retrieved samples from Mars with this mission.”

After its two landings, MMX will leave the surface and send its collected samples back to Earth in a capsule. While the main spacecraft itself will stay in Mars orbit, subsequently performing flybys of Deimos to study that moon from afar, the sample capsule will touch down in an Australian desert in July 2029. Davidson is one of the scientists selected by NASA who will then investigate its samples back on Earth. “By looking at the minerals, we’ll be able to tell if it’s a mineral from Mars or a captured asteroid,” she says.

If the samples prove to be captured asteroids, this finding will pose interesting implications for how they migrated from the outer asteroid belt to Mars. But if they are pieces of Mars, formed by an impact early in its history, that poses its own problems—not least by raising the question of how smaller objects such as these formed around a planet, compared with the size of our own moon around Earth, which is unfathomably larger at some 3,500 km across. “It doesn’t fit the models we have for what material from a giant impact would look like,” Davidson says. “Whatever we figure out, we have to rethink what we’ve assumed we know about these processes.”

MMX and Hope represent a renewed interest in the moons of Mars, which were suggested by the Planetary Society in 2015 as prime locations to begin human exploration of the Red Planet. “If we couldn’t send humans to the surface of Mars, maybe we could send them to rendezvous with Phobos and Deimos,” says Logsdon, a co-author on the Planetary Society report. Now we are closer than ever to working out where they came from, which could help us understand more about how our solar system and its myriad of planets, moons and asteroids came to be. “Understanding how the moons formed is really fundamental to us understanding the dynamics of our solar system,” Davidson says.



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Are Telescopes on the Moon Doomed?

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For radioastronomers, the far side of the Moon could be the last unspoilt refuge in the Solar System. Planet Earth — and all the human-made electromagnetic noise it spews out into space — stays permanently below the horizon, so that any radio observatories positioned there would be free to observe the cosmos without interference.

But an upcoming boom in lunar exploration could put that at risk. In the next ten years or so, the Moon will be the target of hundreds of orbiters and landers, each of which could create radio noise. Researchers voiced their concerns last month at a conference called Astronomy from the Moon: The Next Decades, which took place at the Royal Society in London.

“This is probably the most radio-quiet place in the Solar System, and we need to preserve that,” said Marc Klein Wolt, an astronomer at Radboud University Nijmegen in the Netherlands.

“Will the far side remain dark? You should already be nervous that I’m asking the question,” Joseph Lazio, a researcher at NASA’s Jet Propulsion Laboratory in Pasadena, California, told the conference.

Quiet zone

The lunar far side has enormous potential for many fields, but it holds unique promise for cosmology. Astronomers have mapped the sky using much of the spectrum of electromagnetic waves, from microwaves to visible light and γ-rays. But cosmic radio waves at frequencies below about 100 megahertz are extremely challenging to measure from Earth, because of the planet’s noise. And anything below 30 megahertz is completely off-limits because it is absorbed in the ionosphere — the zone where Earth’s atmosphere meets space. These low-frequency waves, however, carry a treasure trove of information about the first billion years or so of the Universe’s history.

The lunar far side is protected from radio emissions from Earth, and with almost no atmosphere and long, cold nights, it offers a nearly ideal spot from which to explore these epochs.

If all goes according to plan, a small US lander called the Lunar Surface Electromagnetic Experiment (LuSee) Night in 2026 will be the first dedicated cosmology mission to take advantage of those conditions — and it is being designed with that goal in mind. (Chang’e-4, the historic Chinese mission that landed on the far side in 2019, carried a simple radioastronomy antenna. But the mission was not optimized for cosmological observations, so the experiment was marred by radio-frequency interference from the lander itself.)

With funding from both NASA and the US Department of Energy, LuSee-Night will be carried to the far side by a private contractor as part of NASA’s nascent Commercial Lunar Payload Services programme. Its four 3-metre-long antennas, arranged in a cross shape, will attempt to measure the ‘cosmic dawn’, a feature thought to be detectable in the radio spectrum that would reveal the appearance of the Universe’s very first stars.

Noise limitation

Even from the peaceful solitude of the lunar far side, however, LuSee’s cosmic-dawn measurement will be a challenge: the early-Universe signature is 100,000 times weaker than the noise produced by the Galaxy in the same range of frequencies. It will be crucial to limit noise from the spacecraft itself. “The only way to do it is to turn off the lander completely” and pack enough batteries to last the radio receiver through the two-week-long nights, says Stuart Bale, an astrophysicist at the University of California (UC), Berkeley, who is the mission’s principal investigator for NASA. The receiver’s electronics, including the clocks that keep computers running, must be designed to ‘fence’ any emissions to a limited part of the spectrum, Bale says. “We require that all oscillators operate at known frequencies, and with certified frequency stability.” A known, predictable source of noise is easier for experimenters to remove during data processing.

These are relatively simple precautions that all lunar missions could take, including commercial ones, says Bale. If spacecraft are designed to contain any radio-frequency interference, it could greatly reduce the chances of harming future scientific experiments.

Melanie Johnston-Hollitt, former director of the Murchison Widefield Array radio observatory in Western Australia, agrees. At Murchison, which is to be the Australian site of the giant Square Kilometre Array radio telescope, she helped to establish what is probably the world’s largest radio-quiet zone, at more than 500 kilometres across.

Permits are required to carry electronic devices into the site, and “all equipment you take into that area goes through an additional electromagnetic testing process”, to check for unwanted radio emissions, says Johnston-Hollitt, currently a radioastronomer at Curtin University in Perth, Australia. “I can tell you with confidence that you can do that with a cubesat,” she says, referring to the tiny satellites that researchers fear could swarm around the Moon, creating a source of noise.

Even so, “to suppress interference to the level necessary to do precision radioastronomy is incredibly difficult”, says astronomer Andrew Siemion, who leads the Breakthrough Listen search for extraterrestrial intelligence project at UC Berkeley. That work involves looking for signals across a broad range of radio waves — including the gigahertz frequencies at which satellites communicate.

Lunar economy

Astronomers face an uphill struggle. The same technological advances that promise to make the Moon more accessible for their experiments will also make the environment more crowded. More than 250 Moon missions are expected over the coming decade from the space agencies of the United States, Europe, Russia, South Korea, China, Japan, India, Canada and the United Arab Emirates — as well as a host of private companies. That will add up to a US$100-billion ‘lunar economy’, according to Northern Sky Research, a consulting firm in Cambridge, Massachusetts. There are also plans to install a lunar satellite navigation system, which could be a source of noise.

Alanna Krolikowski, a political scientist at Missouri University of Science and Technology in Rolla, thinks that researchers should push for international treaties to protect the Moon. “There is now widespread recognition that we need governance for this forthcoming lunar renaissance,” she told last month’s conference.

The Artemis Accords, an international agreement led by NASA, attempts to provide some guidance to help the agencies involved avoid disrupting each other’s missions. But it is designed mainly to serve the needs of its signatory countries; a better way to regulate the Moon could be to have rules drafted by the United Nations Committee on the Peaceful Uses of Outer Space, Krolikowski said. “The window in which to do that is small — and shrinking.”

This article is reproduced with permission and was first published on March 3, 2023.

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Earthly Microbes Might Survive on Mars for Hundreds of Millions of Years

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One of Earth’s toughest microbes could survive on Mars, lying dormant beneath the surface, for 280 million years, new research has shown. The findings increase the probability that microbial life could still exist on the Red Planet.

Deinococcus radiodurans, nicknamed “Conan the Bacterium,” is one of the world’s toughest microbes, capable of surviving in radiation strong enough to kill any other known life-form. Experiments have now shown that if Conan the Bacterium or a similar microbe existed on Mars, it could survive 33 feet (10 meters) beneath the surface, frozen and dried out, for 280 million years.

In a study led by Michael Daly, who is a professor of pathology at Uniformed Services University of the Health Sciences in Maryland and a member of the National Academies’ Committee on Planetary Protection, scientists tested half a dozen microbes and fungi—all “extremophiles” able to live in environments where other organisms die—to see how long they could survive in an environment that simulated the mid-latitudes of Mars. During the experiments, organisms faced temperatures as low as minus 80 degrees Fahrenheit (minus 63 degrees Celsius) and exposure to ultraviolet light, gamma rays and high-energy protons mimicking the constant bombardment of Mars by solar ultraviolet light and cosmic radiation sleeting down from space. 

After the bacteria and fungi had been exposed to various radiation levels in the experiment, Daly’s team measured how much manganese antioxidants had accumulated in the cells of the microbes. Manganese antioxidants form as a result of radiation exposure, and the more that form, the more radiation the microbes can resist. 

Conan the Bacterium was the clear winner. The researchers found that Conan the Bacterium could absorb as much as 28,000 times more radiation than what a human can survive. This measurement allowed Daly’s team to estimate how long the microbe could survive at different depths on Mars.

Previous experiments, in which Conan the Bacterium had been suspended in liquid water and subjected to radiation like that found on Mars, had indicated that the microbe could survive below the surface of Mars for 1.2 million years. 

However, the new tests, in which the microbe was frozen and dried out to mimic the cold and dry conditions on Mars, suggested that Conan the Bacterium would be able to survive 280 million years on Mars if buried at a depth of 33 feet. This lifespan is reduced to 1.5 million years if buried just 4 inches (10 centimeters) below the surface, and just a few hours on the surface, which is bathed in ultraviolet light.

Mars’ environment 280 million years ago was pretty much the same as it is now—cold and dry—and you have to go back much further to find a time when it was warmer and wet and might have allowed hypothetical Mars life to establish itself in the first place. Daly acknowledges this complication, but thinks there are ways life could have found environments in which to proliferate since Mars’ dramatic climate change. 

“Although Deinococcus radiodurans buried in the Martian subsurface could not survive dormant for the estimated 2 to 2.5 billion years since flowing water disappeared on Mars, such Martian environments are regularly altered and melted by meteorite impacts,” he said in a statement. “We suggest that periodic melting could allow intermittent repopulation and dispersal.”

Consequently, future missions to Mars looking for life might want to target large craters younger than 280 million years. Gale Crater, which NASA’s Curiosity rover is exploring, is 3.8 billion years old; Jezero Crater, where the Perseverance rover is working, is likely a similar age. However, younger craters do abound; for example, Tooting Crater, which is 17 miles (28 km) wide in Amazonis Planitia west of Olympus Mons, is thought to be only hundreds of thousands of years old.

The research also determined why Conan the Bacterium is so resistant to radiation. The scientists found that chromosomes and plasmids, which carry genetic information, in the microbe’s cells are linked together, which keeps these structures aligned and prevents irradiated cells from breaking down until they can be repaired.

This durability means that future missions, such as the European Space Agency’s Rosalind Franklin rover that will dig deep into Mars in search of microbial life, could well find Conan the Bacterium’s Martian cousin, should it exist. 

Sample-return missions could even bring these microbes back to Earth; experiments on the International Space Station have even confirmed that Conan the Bacterium can survive for at least three years in space. However, we’ll need to be careful not to contaminate Earth with Martian microbes.

And future Red Planet missions, both crewed and robotic, also need to be wary of contaminating Mars with Earthly microbes.

“Our model organisms serve as proxies for both forward contamination of Mars, as well as backward contamination of Earth, both of which should be avoided,” Daly said.

While robotic missions to Mars are sterilized before launch, the sterilization process is not perfect and some microbes can still hitch a ride to the Red Planet. If human beings visit Mars, they will bring many more microbes with them, which could escape out into the Martian environment and either destroy the native microbial biosphere or confuse experiments looking for life on Mars. 

As experiments such as this increase the chances of indigenous life existing on Mars, scientists will need to ask additional important questions about how we can protect any potential life that we find there.

The study is detailed in a paper published Tuesday (Oct. 25) in the journal Astrobiology.

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