Astronomy
Annie Jacobsen: 'What if we had a nuclear war?’
Read an extract from Nuclear War: A scenario by Annie Jacobsen
Read an extract from Nuclear War: A scenario by Annie Jacobsen
Scientists identify origin of the 'BOAT' — the brightest cosmic blast of all time
This Week's Sky at a Glance, April 12 – 21
Jupiter is easy to spot, shining low in the west at nightfall. Near it are Uranus and Comet Pons-Brooks, tougher catches that require binoculars or a wide-field telescope — and some finding skills.
The post This Week's Sky at a Glance, April 12 – 21 appeared first on Sky & Telescope.
ESA launches 'Lunar Horizons' Moon mission game in Fortnite
Suit up and get ready to launch on your own amazingly realistic Moon mission! Available now in Fortnite, Lunar Horizons is a vividly immersive experience set on the Moon during a future international mission. Released on 11 April 2024, the game was created by Epic Games, ESA and Hassell, in collaboration with Buendea and Team PWR.
Earth from Space: The Ebro Delta
Did An Ancient Icy Impactor Create the Martian Moons?
The Martian moons Phobos and Deimos are oddballs. While other Solar System moons are round, Mars’ moons are misshapen and lumpy like potatoes. They’re more like asteroids or other small bodies than moons.
Because of their odd shapes and unusual compositions, scientists are still puzzling over their origins.
Two main hypotheses attempt to explain Phobos and Deimos. One says they’re captured asteroids, and the other says they are debris from an ancient impactor that collided with Mars. Earth’s moon was likely formed by an ancient collision when a planetesimal slammed into Earth, so there’s precedent for the impact hypothesis. There’s also precedent for the captured object scenario because scientists think some other Solar System moons, like Neptune’s moon Triton, are captured objects.
Phobos and Deimos have lots in common with carbonaceous C-type asteroids. They’re the most plentiful type of asteroid in the Solar System, making up about 75% of the asteroid population. The moons’ compositions and albedos support the captured asteroid theory. But their orbits are circular and close to Mars’ equator. Captured objects should have much more eccentric orbits.
This illustration shows Phobos and Deimos’ orbits along with the orbits of spacecraft at Mars. The moons’ near-circular orbits don’t support the captured asteroid theory. Image Credit: By NASA/JPL-Caltech – http://photojournal.jpl.nasa.gov/jpeg/PIA19396.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=39982795The moons are less dense than silicate, the most abundant material in Mars’ crust. That fact works against the impact theory. A powerful impact would’ve blasted material from Mars into space, forming a disk of material rotating around the planet. Phobos and Deimos would’ve formed from that material. If they result from an ancient planetesimal impact, they should contain more Martian silica.
Here’s the problem in a nutshell. The captured asteroid theory can explain the moons’ observed physical characteristics but not their orbits. The impact theory can explain their orbits but not their compositions.
Phobos and Deimos look like potatoes more than moons. Image Credit: Left: By NASA / JPL-Caltech / University of Arizona – http://photojournal.jpl.nasa.gov/catalog/PIA10368, Public Domain, https://commons.wikimedia.org/w/index.php?curid=5191977. Right: By NASA/JPL-Caltech/University of Arizona – http://marsprogram.jpl.nasa.gov/mro/gallery/press/20090309a.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=6213773In research presented at the 55th Lunar and Planetary Science Conference, three researchers proposed a different origin story for Phobos and Deimos. They suggest that an impactor is responsible for creating the moons, but the impactor was icy.
The research is titled “THE ICY ORIGINS OF THE MARTIAN MOONS.” The first author is Courteney Monchinski from the Earth-Life Science Institute at the Tokyo Institute of Technology.
If a rocky impactor slammed into Mars, it would’ve created a massive debris disk around the planet. Previous researchers have examined the idea using simulations and found that an impact could’ve created the moons. But the disk created by the impact would’ve been far more massive than Phobos and Deimos combined. The simulations showed that there would’ve been a third, much more massive moon created within Phobos’ orbit that would’ve fallen back down to Mars. But there’s no strong evidence of something that massive striking Mars.
This illustration shows how a giant impact could’ve created Phobos and Deimos. The collision would’ve created a massive debris disk where a third more massive moon formed before falling back to Mars. Image Credit: Antony Trinh / Royal Observatory of BelgiumOther impact studies used basaltic impactors. But those showed that the temperature in the debris disk would’ve been so high it would’ve melted the disk material and destroyed ancient chondritic materials. Since the pair of moons appear to contain those materials, a basaltic impactor is ruled out.
According to the research presented at the conference, an icy impactor can explain Phobos and Deimos’ origins. There are three reasons for that.
The extra disk mass created by a rocky impactor would not be present. Instead, much of the mass in the impactor would’ve been vapourized on impact and escaped the system rather than persisting in the disk and being taken up by the formation of moons. There would’ve been no large third moon and no need to explain how it fell back to Mars.
The second reason concerns the composition of the moons. With abundant water ice in the collision, the temperature in the debris disk would’ve been lower. That would’ve preserved the carbonaceous materials in Phobos and Deimos today. It also can help explain their density and possible porosity. An icy impactor could’ve also delivered water to Mars, and we know Mars was wetter in its past.
The third reason concerns Deimos’ orbit. It’s not synchronous with Mars, and an icy impactor can explain that. With more water ice in the disk, there would’ve been a viscous interaction between the disk’s dust and vapour that extended the disk, allowing Deimos to occupy its orbit.
The researchers used Smoothed Particle Hydrodynamic (SPH) simulations to test the icy impactor idea. They simulated giant impactors with varying quantities of water ice and watched as disks formed around Mars and moons formed in the disk.
They first found that an impactor with any amount of water ice produced a more massive debris disk. It could be because an impactor containing water ice would be larger, though less massive, than one without any ice. That allowed more material to spray from the planet into the disk. It could also be because the water ice absorbs some of the impact energy when it vapourizes. That would cool the disk temperature, lowering the velocities of particles in the disk and making them less likely to escape.
This figure from the research shows that any amount of ice in an impactor increases the size of the debris disk. Image Credit: Monchinski et al. 2024. LPSCVarying the ice content in the impactor also affected the makeup of the disk. Different amounts of ice lead to disks with different amounts of Martian rock and impactor rock in the disk.
This graph from the study shows impactor ice content (x-axis) affects the debris disk composition. Image Credit: Monchinski et al. 2024. LPSCThe temperature in the disk is a critical part of this. Different amounts of water ice in the impactor change the disk temperature and what types of materials in the disk would melt. Impactors with more than 30% ice create disk temperatures too low to melt silicates. Perhaps more tellingly, impactors with more than 70% ice result in a disk temperature too low to alter or destroy chondritic material, which both Phobos and Deimos are expected to contain.
According to the researchers, an icy impactor can also explain other features. “The existence of water in the impact-generated disk also suggests that water may condense, accounting for the possible water-ice content of the moons,” they write.
Ultimately, the researchers say an icy impactor with 70% to 90% water ice mantles can explain the pair of moons.
“The best case for reproducing the moons’ proposed compositions are the 70% and 90% water-ice mantle impactor cases, as they allow for low disk temperatures and more chances for chondritic materials to survive,” they explain.
Unfortunately, that may not be realistic. “In our current solar system, an object with around 70% or 90% water-ice content is not exactly realistic, as the object with the highest amount of water content in our current solar system, Ganymede, is only about 50% water,” they write.
The ESA’s Mars Express orbiter captured this image of Phobos over the Martian landscape in this image taken in November 2010. Irregularly shaped and only 27 km long, Phobos is actually much darker (due to its carbon-rich surface) than is apparent in this contrast-enhanced view. Image Credit: ESA / DLR / G. neukumBut could things have been different in the past? Samples from asteroid Ryugu suggest that its parent body could’ve been up to 90% water. That number is based on the types of minerals in Ryugu. But unfortunately, scientists don’t now for sure. Ryugu’s parent body could have contained as little as 20% water.
But it’s at least plausible that early in the Solar System’s life, an impactor with 70% water ice could have existed. If so, then the icy impactor scenario could be a robust theory to explain the origins of Phobos and Deimos.
“This impactor would have come from the outer solar system around the time of giant planet instability,” the authors write. During that time, outer Solar System bodies were perturbed and sent flying into the inner Solar System. But in this case, the impact’s timing needs to be constrained by Phobos’ and Deimos’ formation ages.
Scientists need more evidence to deepen their understanding of Mars and its moons. Japan’s Martian Moons eXploration (MMX) mission will provide that. MMX’s mission is to return a sample of Phobos to Earth. The goal is to determine if it is a captured asteroid or the result of an impact.
Unfortunately, JAXA just delayed MMX’s launch. It was scheduled to launch in September 2024 but has been delayed until 2026. That means we won’t get samples until 2031 instead of 2029.
JAXA has completed successful sample return missions, so they have the expertise to bring a piece of Phobos back to Earth. If scientists can determine how Phobos and Deimos formed, it’ll be part of a much larger, detailed picture of how the Solar System formed.
It’ll be worth it if we have to wait a couple extra years.
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Embryos pause development when nutrients are low — and now we know how
Embryos pause development when nutrients are low — and now we know how
My formal 2024 solar eclipse apology
Achoo! Baby star 'sneezes' tell astronomers a lot about their development
Scientists Found a Way to Supercharge Cancer-Fighting Cells
The bioengineered immune players called CAR T cells last longer and work better if pumped up with a large dose of a protein that makes them resemble stem cells
How Will EPA’s New Rule about ‘Forever Chemicals’ Protect Your Drinking Water?
A new EPA rule will limit PFASs, or “forever chemicals,” in your drinking water for the first time. Here’s what that means for you
NASA’s Next Solar Sail is About to Go to Space
Everyone knows that solar energy is free and almost limitless here on Earth. The same is true for spacecraft operating in the inner Solar System. But in space, the Sun can do more than provide electrical energy; it also emits an unending stream of solar wind.
Solar sails can harness that wind and provide propulsion for spacecraft. NASA is about to test a new solar sail design that can make solar sails even more effective.
Solar pressure pervades the entire Solar System. It weakens with distance, but it’s present. It affects all spacecraft, including satellites. It affects longer-duration spaceflights dramatically. A spacecraft on a mission to Mars can be forced off course by thousands of kilometres during its voyage by solar pressure. The pressure also affects a spacecraft’s orientation, and they’re designed to deal with it.
Though it’s a hindrance, solar pressure can be used to our advantage.
A few solar sail spacecraft have been launched and tested, beginning with Japan’s Ikaros spacecraft in 2010. Ikaros proved that radiation pressure from the Sun in the form of photons can be used to control a spacecraft. The most recent solar sail spacecraft is the Planetary Society’s LightSail 2, launched in 2019. LightSail 2 was a successful mission that lasted over three years.
The Red Sea and the Nile River, from the LightSail 2 spacecraft. LightSail 2 was a successful demonstration mission that lasted more than two years. Image Credit: The Planetary Society.Solar sail spacecraft have some advantages over other spacecraft. Their propulsion systems are extremely lightweight and never run out of fuel. Solar sail spacecraft can perform missions more cheaply than other spacecraft and can last longer, though they have limitations.
The solar sail concept is now proven to work, but the technology needs to advance for it to be truly effective. A critical part of a solar sail spacecraft is its booms. Booms support the sail material; the lighter and stronger they are, the more effective the spacecraft will be. Though solar sails are much lighter than other spacecraft, the weight of the booms is still a hindrance.
“Booms have tended to be either heavy and metallic or made of lightweight composite with a bulky design – neither of which work well for today’s small spacecraft.”
Keats Wilkie, ACS3 principal investigator, NASANASA is about to launch a new solar sail design with a better support structure. Called the Advanced Composite Solar Sail System (ACS3), it’s stiffer and lighter than previous boom designs. It’s made of carbon fibre and flexible polymers.
Though solar sails have many advantages, they also have a critical drawback. They’re launched as small packages that must be unfurled before they start working. This operation can be fraught with difficulties and induces stress in the poor ground crew, who have to wait and watch to see if it’s successful.
This image shows the ACS3 being unfurled at NASA’s Langley Research Center. The solar wind is reliable but not very powerful. It requires a large sail area to power a spacecraft effectively. The ACS2 is about 9 meters (30 ft) per side, requiring a strong, lightweight boom system. Image Credit: NASAACS3 will launch with a twelve-unit (12U) CubeSat built by NanoAvionics. The primary goal is to demonstrate boom deployment, but the ACS3 team also hopes the mission will prove that their solar sail spacecraft works.
To change direction, the spacecraft angles its sails. If boom deployment is successful, the ACS3 team hopes to perform some maneuvers with the spacecraft, angling the sails and changing the spacecraft’s orbit. The goal is to build larger sails that can generate more thrust.
“The hope is that the new technologies verified on this spacecraft will inspire others to use them in ways we haven’t even considered.”
Alan Rhodes, ACS3 lead systems engineer, NASA’s Ames Research CenterThe ACS3 boom design is made to overcome a problem with booms: they’re either heavy and slim or light and bulky.
“Booms have tended to be either heavy and metallic or made of lightweight composite with a bulky design – neither of which work well for today’s small spacecraft,” said NASA’s Keats Wilkie. Wilke is the ACS3 principal investigator at Langley Research Center. “Solar sails need very large, stable, and lightweight booms that can fold down compactly. This sail’s booms are tube-shaped and can be squashed flat and rolled like a tape measure into a small package while offering all the advantages of composite materials, like less bending and flexing during temperature changes.”
ACS3 will launch from Rocket Lab’s launch complex 1 on New Zealand’s north island. Image Credit: Rocket LabACS3 will be launched on an Electron rocket from Rocket Lab’s launch complex in New Zealand. It’ll head for a Sun-synchronous orbit 1,000 km (600 miles) above Earth. Once it arrives, the spacecraft will unroll its booms and deploy its sail. It’ll take about 25 minutes to deploy the sail, with a photon-gathering area of 80 square meters, or about 860 square feet. That’s much larger than Light Sail 2, which had a sail area of 32 square meters or about 340 square feet.
As it deploys itself, cameras on the spacecraft will watch and monitor the shape and symmetry. The data from the maneuvers will feed into future sail designs.
“Seven meters of the deployable booms can roll up into a shape that fits in your hand,” said Alan Rhodes, the mission’s lead systems engineer at NASA’s Ames Research Center. “The hope is that the new technologies verified on this spacecraft will inspire others to use them in ways we haven’t even considered.”
ACS3 is part of NASA’s Small Spacecraft Technology program. The program aims to deploy small missions that demonstrate unique capabilities rapidly. With unique composite and carbon fibre booms, the ACS3 system has the potential to support sails as large as 2,000 square meters, or about 21,500 square feet. That’s about half the area of a soccer field. (Or, as our UK friends mistakenly call it, a football field.)
With large sails, the types of missions they can power change. While solar sails have been small demonstration models so far, the system can potentially power some serious scientific missions.
“The Sun will continue burning for billions of years, so we have a limitless source of propulsion. Instead of launching massive fuel tanks for future missions, we can launch larger sails that use “fuel” already available,” said Rhodes. “We will demonstrate a system that uses this abundant resource to take those next giant steps in exploration and science.”
A solar flare as it appears in extreme ultraviolet light. The Sun is a free source of energy that’s not going away anytime soon, yet it’s also hazardous. Credit: NASA/SFC/SDOSolar sail spacecraft don’t have the instantaneous thrust that chemical or electrical propulsion systems do. But the thrust is constant and never really wavers. They can do things other spacecraft struggle to do, such as taking up unique positions that allow them to study the Sun. They can serve as early warning systems for coronal mass ejections and solar storms, which pose hazards.
The new composite booms also have other applications. Since they’re so lightweight, strong, and compact, they could serve as the structural framework for lunar and Mars habitats. They could also be used to support other structures, like communication systems. If the system works, who knows what other applications it may serve?
“This technology sparks the imagination, reimagining the whole idea of sailing and applying it to space travel,” said Rudy Aquilina, project manager of the solar sail mission at NASA Ames. “Demonstrating the abilities of solar sails and lightweight, composite booms is the next step in using this technology to inspire future missions.”
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