Tiny NEA Scout Solar Sail Mission to Chase Asteroid

NEA Scout will hitch a ride to an asteroid on the Artemis 1 Moon mission.

Tucked away on the long-awaited, historic launch of NASA’s Space Launch System (SLS) this April is a small, shoebox-sized mission mission that with use an innovative solar sail technology, to chase down a school-bus sized asteroid.

The mission is NEA (Near Earth Asteroid) Scout. Folded up and stowed away, the entire payload fits in a small 10 cm x 20 cm x 30 cm 6U cubesat. Once in space and unfurled, the tiny spacecraft will deploy solar panels for power, and four 7.3-meter long rods will support a 9.3-meter square sail for maneuvering and propulsion. Then, NEA Scout will use solar pressure to gradually depart the Earth-Moon system to the target.

The target asteroid 2020 GE is an intriguing space rock. Discovered on the night of March 12^th, 2020 by the University of Arizona’s Catalina Sky Survey, the asteroid is in a 2.3 degree inclined orbit relative to the ecliptic, orbiting the Sun once every 368 days, meaning that 2020 GE visits the Earth every few years. It has two particularly close (<0.005 AU or 750,000 km, or 2.5 times the Earth-Moon distance) passes in the 21^st century in 2024 and 2068. 2020 GE is 5-15 meters across, on the large end of the scale.

The orbit of asteroid 2020 GE. Credit: NASA-JPL.

“2020 GE chose us!” Principal Investigator Julie Castillo-Rogez (NASA-JPL) told Universe Today concerning the selection of a target for NEA Scout. “The pool of targets reachable for any launch window is small. There are a lot of NEOs, but those that can be accessed with our spacecraft need to meet a number of criteria. First, their position needs to be relatively well known (within a few 1000s of kilometers). We also need to encounter the target when it is less than 1 AU (astronomical unit) from Earth because our telecommunication system is limited in performance (small antenna). Lastly, our total mission duration needs to be shorter than 2.5 years because some the components we use in the flight system have a limited lifetime.”

“Thanks to the introduction of new observatories over the past decade and the help of the astronomical community, we’ve always had a couple of targets available for any launch window.”

The team plans to encounter 2020 GE during the September 8th, 2023 close pass for flyby, when the asteroid is 0.038 AU from the Earth. This will be the smallest target ever visited, and a 30 meters per second, the slowest asteroid flyby yet. This will also represent our first good look at a small near-Earth asteroid, in the pristine environment of space. This sort of approach and rendezvous technology could prove vital, should we ever have to deflect one of these space rocks out of harm’s way. A very similar-sized asteroid exploded over the Russian city of Chelyabinsk the day after Valentine’s Day in 2013.

“2020 GE is between 5-15 meters large, so one at least one order of magnitude smaller than Hayabusa’s target Itokawa (~210 meters in its smallest dimension).” Says Castillo-Rogez. “As another point of comparison, the OSIRIS-REx target Bennu is about 510 meters in its smallest dimension.”

NEA Scout was developed by NASA’s Advanced Explorations Systems Division at the Marshall Spaceflight Center, to test key technologies in a small package. The mission will carry a small camera (NEACam) with a resolution down to 10 cm (4 inches) per pixel, so we should get some pretty good images of 2020 GE, in an effort to understand if its a solid chunk of rock, or a ruble pile asteroid.

“NEAScout will carry a small imager. Its mass is about 1 lbs. Although it is very small, we demonstrated that its performance meets our requirements for science observations.” Says Castillo-Rogez. “We will launch in the Spring, spend a few months in the Earth-Moon region and start the interplanetary cruise in August 2022 (required to catch the asteroid). The flyby of the target will be in November 2023. We will start searching for it about one month prior to encounter. After the flyby, we will downlink the data in a few months (at least 3 and up to 6).”

A Brief History of Solar-Sailing the Solar System

Though the idea of solar sailing has long held promise, the road to practical use has been a tough one. The Planetary Society lost its very first effort at deploying a solar sail on the Cosmos 1 mission in 2005, when the Volna rocket launched from a Russian submarine failed shortly after launch. The Society fared better with Lightsail-2 in 2019. The Japanese Aerospace Agency (JAXA) also had better luck with IKAROS in 2010, deployed from the Venus-bound Akatsuki mission. The NanoSail-D mission in 2010 also showed the viability of using a solar/drag sail for a controlled reentry.

To be sure, Artemis-1 and the inaugural launch of SLS will be a historic one, and a first step in humanity’s return to the Moon. NEA Scout is one of 10 smallsat missions taking advantage of the Artemis 1 launch, headed out into cis-lunar space and back.

Artemis 1 orbit and smallsat deployment phase. Credit: NASA

As of writing this, SLS is slated to launch in April 8th-22nd, with a backup window in May from the 7th-21st 2022. The NEA Scout and other smallsat payloads are tucked away inside the Orion stage ring adapter of the booster.

Cubesats nestled inside the Orion ring adapter. Credit: NASA/Cory Huston

2022 also sees commercial Moon landing missions from Astrobotics and Intuitive Machines, as part of NASA’s Commercial Lunar payload Services (CLPS) program. NASA will also launch Cislunar Autonomous Positioning System Technology Operations and Navigation Experiment (CAPSTONE) in March, a pathfinder mission for the crewed Lunar Gateway platform, also part of the Artemis initiative.

Stacking SLS for Artemis 1. Credit: NASA/Cory Huston

Things are about to get busy in cis-lunar space in 2022, and NEA Scout will be a mission to watch in the coming years.

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Latest Hubble Image Shows the Star-Forming Chamaeleon Cloud

Stars form inside vast collections of molecular hydrogen called molecular clouds, sometimes called stellar nurseries or star forming regions. Instabilities in the clouds cause gas to collapse in on itself, and when enough material gathers and the density reaches a critical stage, a star begins its life of fusion.

But molecular clouds aren’t always alone. They often exist in association with other clouds, and astronomers call these formations Cloud Complexes. The Chamaeleon Cloud Complex (CCC) is one of the closest active star forming regions to Earth. It’s further divided into three substructures called dark clouds, or dark nebula. They are Chamaeleon 1 (Cha1), Chamaeleon 2, and Chamaeleon 3.

NASA created a new composite image of Chamaeleon 1 based on Hubble images, and the vivid panorama brings Chamaeleon I to life.

The CCC is a massive star-forming region (SFR) that occupies most of the Chamaeleon constellation. The complex is about 65 light-years wide is about 160 parsecs (522 light-years) away.

There’s a lot going on in this image: dark dusty molecular clouds shelter young stars as they form, other bright blue young stars light up striking reflection nebula, and jets of ionized gas slamming into nearby dust clouds at hundreds of kilometres per second create bright clumps of nebulosity called Herbig-Haro (HH) objects.

When young stars are still forming and accreting material from their surrounding disks, they can emit powerful jets of ionized gas. The jets are also called MHOs—Molecular Hydrogen emission-line Objects. The star emits the jets from its poles and they create MHOs aligned with the star’s rotational axis. Sometimes there are several MHOs near a single star.

In this Hubble image, a protostar sits in the white-orange cloud near the bottom. The narrow jets of ionized gas in this part of Cha 1 create the Herbig-Haro object HH 909A. HHs don’t last long and astronomers can watch as they change over the years.

This is an older Hubble Space Telescope image of the ethereal object known as HH 909A. These speedy outflows collide with the slower surrounding gas, lighting up the region. Image Credit: NASA, ESA, and P. Hartigan (Rice University)

These Hubble images aren’t just for visual enjoyment. Everything about young stars is interesting to astronomers, and Hubble’s succeeded at imaging the environments around young stars, including Herbig-Haro objects. This video shows how the Herbig-Haro HH 46, which isn’t in Cha1, changed in 14 years.

HH 909A will undergo changes similar to the ones in the video. In fact, lots will change inside Cha1, and young stars will drive most of that change. When stars emerge from their dark nebula as fully-formed balls of fusion, their powerful stellar winds will shape the gas that surrounds them. The bright blue nebula is an example of the interaction between the young stars and the gas.

In the nebula in the leading image, the star isn’t energetic enough to ionize the gas. If it were, the gas would then emit its own light as an emission nebula. Instead it’s a reflection nebula, where the light from the star is scattered, making the dust in the cloud visible. Reflection nebulae are often blue for the same reason our sky appears blue: blue light is scattered more efficiently. The scattering is called Rayleigh Scattering after the discoverer, British physicist Lord Rayleigh.

Our Sun was born the same way the stars in the Hubble image were: inside a molecular cloud. Stars form in groups inside these clouds, and our Sun may have had thousands of siblings. In its earlier epochs, the Sun was part of a star cluster, the same types of clusters we see in the sky today.

This is a Hubble image of a giant cluster of thousands of stars called Westerlund 2. Our own Sun was born in a cluster like this and had thousands of siblings. Image Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team

The Sun’s siblings drifted away from one another, and the Sun dispersed the gas and dust in its immediate surroundings long ago. Its stellar wind spread the gas and dust back into the ISM, to eventually be taken up in another molecular cloud and begin the star formation cycle all over again.

But at one time in its early days, our Sun may have had its own reflection nebula. That would’ve been a remarkable sight.

We’ll never know exactly where our Sun formed and whether it had a nebula, or what that nebula might have looked like. But we can gaze at this Hubble image and wonder about it. Each time we look at young stars forming in a cloud complex like Cha 1, with its Herbig-Haro objects, its nebula, and its jets of ionized gas, it’s a glimpse back in time to our own beginnings.

Because, somewhere in the disk of gas and dust swirling around the young Sun, surrounded by thousands of stellar siblings, embedded in all that raucous mayhem, a rocky planet began to take shape.

More:

• Press Release: Hubble Examines a Star-Forming Chamaeleon
• All Things Hubble: Hubblesite
• Universe Today: Nearby Supernovae Exploded Just a few Million Years Ago, Leading to a Wave of Star Formation Around the Sun

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Finally, a Practical use for Space-Based Power Beaming. Sending Power to Satellites in Shade

Power beaming is one of those technologies that can completely change the world.  Almost unlimited power wherever it is needed, whenever it’s needed, is literally a technology straight out of science fiction.  Researchers have been working on the technology for decades at this point, but there has been little commercial headway so far, so what is holding this revolutionary technology up?  A “killer app” would certainly help move it along – and that is what a team from Space Power, a private company, and the University of Surrey think they have found in the form of powering other microsatellites.

All current CubeSats and other microsatellites have to have their own power system. Sometimes they are powered by solar panels, other times by batteries, and even more rarely by radioisotope thermoelectric generators (RTGs).  These solutions have limitations, including limited lifetimes (batteries) or limited size (RTGs, solar panels).  Any improvement in the way microsatellites can be powered would be welcomed by the burgeoning satellite industry.

Concept of a space-based power beaming satellite.
Credit – ESA

That improvement is the focus of a SPRINT (SPace Research and Innovation Network for Technology) grant that provided £7.4 million to a public-private partnership involving the University of Surrey’s Department of Physics and Space Power, a private company supported by the OI Space Incubator.  The grant comes on the heels of a feasibility study the two entities produced that proved the concept of using a laser to send power from one satellite to another.  

The current goal of the grant is to increase “small satellite operating efficiencies by a factor of between 2x-5x,” according to a press release from the University.  The team will build a practica prototype that could eventually fly as part of a launch and demonstrate the power beaming technology in situ.  If successful, private money should surely follow to support a commercial end goal.  And with the increasing need for commercial satellites will come increased commercial opportunities for novel ways to power them. With a goal of creating commercially available products by 2025, the team at Space Power and the University of Surrey have a lot of work ahead of them.

Learn More:
University of Surrey – Revolutionizing satellite power using laser beaming
Space Power
ExecutiveGov.com – Space Power, University of Surrey Develop Wireless Satellite Power Beaming Technology
UT – The Navy is Testing Beaming Solar Power in Space

Lead Image:
Concept image showing how a power satellite might power other microsatellites with solar panels.
Credit – Space Power

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Astronomers Finally Find a Second Asteroid in Earth’s Trojan Belt

Earth has a new companion. Asteroid 2020 XL5, a newly discovered kilometer-wide carbonaceous space rock, has been discovered at Earth’s L4 Lagrange point – a place where the gravitational forces of Earth and the Sun balance out, creating a stable point in which objects can become trapped. A new paper published this week in Nature Communications confirms that 2020 XL5 will be stuck at L4 for at least another 4000 years, shepherded silently through the Solar System by the gravitational tug of our home planet.

This is only the second Earth Trojan ever discovered – the first was found in 2010 – but other planets have plenty of them. Jupiter, which has been throwing its weight around in the Solar System for eons, has thousands of trojans, so many that the asteroid swarms at Jupiter’s L4 and L5 points rival the number of objects in the main asteroid belt itself. A mission to study Jupiter’s Trojans, named Lucy, launched in October and will arrive at Jupiter’s L4 point in 2027. Understanding what these captured asteroids are made of will help researchers build a clearer picture of the early Solar System.

Earth’s Lagrange points, where objects (known as Trojans) are able to remain in stable or semi-stable orbits. The newly discovered Earth Trojan 2020 XL5 was found at Earth’s L4 point. Credit: NASA/WMAP Science Team.

While its hoard is impressive, Jupiter does not have a monopoly on trojan asteroids. Neptune has 29 known trojans, and even Mars, at three-fifths of Earth’s size, has over a dozen of them in its Lagrange points.

So why does Earth have so few? Well, first of all, there are probably more out there, we just haven’t found them yet. Earth Trojans are notoriously hard to see because, from our perspective, we have to stare nearly directly towards the Sun to find them, making them near impossible to pick out in the glare. It doesn’t help that c-type asteroids like 2020 XL5 tend to have low albedo’s, reflecting very little light. This combination makes spotting Earth Trojans a difficult challenge.

So how was 2020 XL5 discovered? The trick is to time the observations carefully. There is a short period just before sunrise and just after sunset when the Sun is blocked by the horizon, but the Lagranges points are still visible in the sky. This isn’t an ideal observing situation, and the window of opportunity doesn’t last long, but it’s enough to take a quick look.

Using this method, astronomers used the Pan-STARRS1 survey, based in Hawaii, to find the object back in December of 2020. At the time, it was clear that 202 XL5 might possibly be an Earth Trojan, but it took until this recent study to confirm it. The data shows that this is a ‘transient trojan,’ meaning it did not begin in Earth’s L4 point, but was rather captured, and it won’t remain there forever either, eventually being bumped out to roam free once again. This isn’t likely to happen for a while, though, and it will remain in the L4 neighborhood for at least the next four millennia.

The attempt to find Earth Trojans doesn’t only rely on Earth-based telescopes. Space probes have visited Earth’s L4 and L5 points in search of previously unseen objects in-situ. For example, NASA’s OSIRIS-REx spacecraft carried out a survey in the L4 region, while the Hayabusa2 spacecraft visited L5 on its way to asteroid Ryugu. Neither mission detected new Earth Trojans, but they helped create population constraints regarding the number and size of the asteroids that might be there.

The search for more Earth Trojans continues. As the paper’s lead author Toni Santana-Ros explains, “asteroids are time capsules from the earliest days of our Solar System and can teach us lots about the era of planetary formation. Earth Trojans are particularly interesting, as they could be leftover material from the formation of Earth. Even if they come from far away instead, their relatively stable orbits at Earth’s Lagrange points could still make them ideal destinations for a spacecraft mission.”

When asked what’s next for the team, Santana-Ros replied, “This discovery strongly encourages us to keep searching for new Earth Trojans. Finding an Earth Trojan made of material leftover from Earth’s formation would be incredibly helpful for unraveling many secrets of the early Solar System.”

Learn More:

“Newly discovered asteroid just second of its kind” ESA.

T. Santana-Ros et al. “Orbital stability analysis and photometric characterization of the second Earth Trojan asteroid 2020 XL₅” Nature Communications.

Featured Image: rendering of Earth Trojan 2020 XL5. Credit: NOIRLab/NSF/AURA/J. da Silva/Spaceengine

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A Chinese Space Tug Just Grappled a Dead Satellite

A Chinese satellite pulled a defunct navigation satellite out of the way of other satellites on January 22nd. The satellite, called SJ-21, appeared to operate as a space tug when it grappled onto the navigation satellite from the Chinese CompassG2 network. The operation details didn’t come from Chinese authorities but a report by ExoAnalytic Solutions, a commercial space monitoring company.

Chinese authorities are tight-lipped about the operation, but what can observations tell us about Chinese capabilities?

Earth’s geosynchronous orbit is crowded, so on the face of it, having one less piece of space debris is a good thing for all satellite operators. But people can get suspicious when China does something like this. Is suspicion warranted?

The details of the operation are in a report from ExoAnalytic Solutions. They presented them in a webinar hosted by the Center for Strategic and International Studies (CSIS) and the Secure World Foundation (SWF.) Brian Flewelling from ExoAnalytic presented the report.

ExoAnalytic Solutions owns and operates over 30 observatories and over 300 telescopes worldwide. The company says they monitor the full 360 degrees of the GEO belt and the graveyard region. Their Global Telescope Network is the world’s largest network of optical telescopes. According to the company’s website, they provide “…ubiquitous, automated, real-time space domain awareness for space superiority.”

This is one of the ExoAnalytic Solutions observing facilities. The company has over 30 observatories and more than 300 telescopes worldwide. Image Credit: ExoAnalytic Solutions.

Here’s what happened, according to ExoAnalytic Solutions.

On January 22nd, SJ21 went absent from its orbital slot for several hours. Before that, it performed close proximity operations with the defunct CompassG2 satellite, moving closer and closer. SJ21 docked with the dead satellite, but ExoAnalytics didn’t observe the actual docking. The docking took place in daylight when the company’s telescopes couldn’t image the satellite. ExoAnalytics reacquired SJ21 after it pulled the inoperative satellite out of geosynchronous orbit.

This video from ExoAnalytic Solutions explains their observations.

The China Aerospace Science and Technology Corporation (CASC) operates JS-21 (Shijian-21), but they haven’t been very open about the satellite’s operations and capabilities. They launched the satellite on October 24th, and China’s Xinhua news agency said, “The satellite will be mainly used to test and verify space debris mitigation technologies.”

Space debris is a growing problem, so any efforts to mitigate it are welcome. But China is tight-lipped about it. Compare their lack of details with other countries’ space debris mitigation efforts.

The ESA has a comprehensive web presence detailing its ongoing efforts to deal with space debris. Individual articles describe using drag sails to deorbit dead satellites, graphics explain the problem, and interviews with experts flesh out the whole issue. NASA is similar. The Canadian Space Agency also practices openness, especially when their a piece of space debris struck the Canadarm2 robotic arm in April 2021.

The Canadarm2, the Canadian-made robotic arm used on the International Space Station, suffered “limited” damage after it was hit by space debris in 2021. (NASA/Canadian Space Agency)

The United Nations’ Space Debris Mitigation Guidelines apply to all UN member states, including China. It can be challenging for citizens of western democracies to understand why China would be so secretive about something as innocuous as space debris mitigation. But China practices secrecy and obfuscation as a matter of course.

What do SJ-21’s operations mean?

First of all, this isn’t the first time SJ-21 has been in the news. In November, it attracted attention when the US Space Force’s 18th Space Control Squadron watched as the satellite orbited alongside another object. The 18th SCS said the object was probably a spent apogee kick motor. Typically, a rocket puts a satellite into a transfer orbit, and an apogee kick motor on the satellite itself provides the final thrust to bring the satellite into geostationary orbit.

China never confirmed it.

Other space agencies are concerned that China could use SJ-21 to interfere with operational satellites from other countries. Whether or not that’s China’s intent, the suspicion won’t go away.

The US Air Force’s China Aerospace Institute is a think tank that examines China’s activities in space. The Institute released a report in December 2021 focusing on SJ-21. “… one can reasonably argue that SJ-21 is probably going to be China’s second On-Orbit Servicing, Assembly, and Manufacturing (OSAM) practice-series satellite (Shijian) in GEO,” the report says.”

“One could also reasonably expect SJ-21 to advance work China has already done in lower orbits to practice rendezvous and proximity operations (RPOs) and the use of a robotic arm,” the report says. “This time, China might practice using multiple arms, a different type of debris mitigation technology such as that needed for refuelling or
deorbiting, or a combination of those, based on Chinese academic publications…”

But the report also says that “China’s activities in OSAM have not been examined in-depth to date.”

China is framing SJ-21 as part of their On-Orbit Servicing, Assembly, and Manufacturing (OSAM) operations. But is there something more to it?

In an article at Breaking Defense, Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, pointed out something unusual in SJ-21’s activities. McDowell said that the satellite’s orbit “…is highly elliptical, ranging from 36,076 km in altitude to 38,886 km.“

Satellites are moved into the graveyard orbit when it’s easier to boost them into that orbit than to deorbit them. Satellites can stay in the graveyard orbit for millions of years. The graveyard orbit is about 300 km above the geostationary orbit, about 36,000 km. But JS-21 moved its dead passenger into an elliptical orbit that takes it well beyond that.

In order to eliminate collision risk, GEO satellites should be moved out of the geostationary ring at the end of their mission. Their orbit should be raised by about 300 km, according to the ESA, which is considered a safe distance to avoid future interference with active GEO spacecraft. Image Credit: ESA

“Usually, GEO graveyard raising is done more symmetrically,” McDowell explained in the Breaking Defense article.

ExoAnalytic Solutions reported that SJ-21 is now back in a geosynchronous orbit. So was this a harmless debris mitigation maneuver? If it was, why hasn’t China said so? Do they like keeping other countries in the dark, just in case? Is something potentially sinister going on? Asking these questions isn’t to invite conspiracy theories. This is global politics.

China isn’t the only one to develop and employ satellites like this. The Northrop-Grumman company developed their MEV-1 (Mission Extension Vehicle 1) satellite to help mitigate space debris. But the MEV-1 is designed to dock with customers’ satellites and re-fuel them to extend their lives. They can’t use that capability offensively. Could SJ-21 be a precursor to offensive satellite operations? People are reluctant to say that publicly, but must be wondering behind closed doors.

Northrop-Grumman made a promotional video of their MEV-1 satellite.

This could all be much ado about nothing. Many space agencies are putting more resources into space debris mitigation. It’s sensible operationally, scientifically, and economically. Maybe SJ-21 is purely a business venture, and China is keeping their cards close to their chest to protect any hoped-for economic advantage. But NASA, the ESA, and others are far more open about their activities.

Why so tight-lipped, China?

Maybe they’re just following Sun-Tzu’s advice when he said, “Let your plans be dark and impenetrable as night …”

More:

• ExoAnalytic Solutions
• Breaking Defense: China’s SJ-21 ‘tugs’ dead satellite out of GEO belt: Trackers
• Universe Today: Satellite Debris Forces Space Station To Evade Threat Hours Before Collision Risk

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China’s Rover Finds That Regolith on the Moon’s far-Side is Stickier Than the Near-Side

We’re never able to see the far side of the moon from the Earth, but that doesn’t mean it’s that different.  Recently rovers and satellites have started exploring the lesser-known side of the moon.  They found a slightly different geology than that discovered on the near side, which might have implications for navigating the far side in the future.

China’s Chang’E-4 mission landed on the far side of the moon over three years ago in humanity’s first successful attempt at doing so.  Since then, it has been trundling around the surface, making discoveries such as a strange-looking rock and some of the moon’s mantle on its surface.  

A map of the path the rover has taken, as well as the wheel slippage rates on each day of travel.
Credit – Ding et al.

Now a new paper discusses a topic that is an unusual data source – how the Yutu-2 rover that is part of the Chang’E-4 mission has been moving.  Published in Science Robotics, the paper discusses the various trials and tribulations that the rover has experienced while navigating a side of the moon that radio signals from Earth cannot directly reach.

The signal bouncing required to communicate Yutu-2 hasn’t slowed the rover down, though.  What has slowed it down is its wheels slipping and sliding in some spots and getting clogged with dirt in others.  Yutu-2 appears to be navigating a series of gentle slopes that regularly cause slight slippage of its wheels, which is caused by material similar in texture to sandy loam on Earth.

An example of some of the cohesive regolith that stuck to the rover’s wheels.
Credit – Ding et al.

Even with all the slipping and sliding, there have been noticeably more dirt clumps attaching themselves to the rover’s wheels than there have been at other lunar landing sites.  This would imply a slightly higher cohesion to the regolith than the near side.  There could be several different explanations for this, including the far side getting blasted by more solar radiation or something local to the geology of the far side region.`

Other exciting finds include small impact craters along the route Yutu-2 took, some of which had markings that indicated “secondary impact events.”  Those happen when a meteorite or other small object impacts in a larger crater that was previously formed. In addition, some of the material at the bottoms of those craters were a “high reflectance,” making them attractive to any future explorers.

Open Space forum about China’s plans for the moon.

Ultimately, the differences between what Yutu-2 has found on the far side and what Apollo and other missions located on the near side were relatively minor.  The moon appears to be the moon, no matter what side you’re on.  That makes it slightly easier for any future human explorers, but there might still be some other mysteries on the far side to unlock – if only humanity sends some more explorers there.

Learn More:
Science Robotics – A 2-year locomotive exploration and scientific investigation of the lunar farside by the Yutu-2 rover
New Scientist – Yutu-2 lunar rover finds sticky soil on the far side of the moon
Astronomy.com – The Moon’s farside has sticky soil, Yutu-2 finds
UT – China’s Yutu-2 Rover has now Traveled Over 345 Meters Across the Surface of the Moon

Lead Image:
Image of the Yutu-2 rover from the Chang’E 4 mission
Credit – CNSA

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Astronomers Lined up Under an Asteroid’s Shadow to Measure its Size Precisely

Astronomers will go to great lengths for science. Recently, dozens of astronomers had the misfortune of traveling to one of the most tempting locales in the southwestern US – Las Vegas.  But they weren’t there for the city’s bright lights – they were there to observe a very dim light of a star thousands of light-years away.  And what they specifically wanted to see was the light from that star blink out for a few seconds.  That lack of light provided the exact kind of data they needed to help them determine the size of Eurybates, one of the Trojan asteroids that will be the focal point of NASA’s Lucy mission.

What the scientists were looking for was an occultation.  Most people know the most common form of this phenomenon – an eclipse.  But occultations can happen with any background star and can be caused by any foreground object.  Calculating where these minor occultations of stars by asteroids will occur takes a significant amount of orbital mechanics and processing power.  The Earth itself has to be aligned correctly, and the asteroids and stars have to line up just right and be big enough. 

NASA Goddard video describing the occultation data collection program.
Credit – NASA Goddard YouTube Channel

If an asteroid is big enough, it will cause the equivalent of a shadow in the star’s light, which can be used as a proxy measurement for its size.  The shadow Eurybates caused was approximately 64 km (40 mi) wide, but scientists didn’t know its precise dimensions.  So they set up observational sites around the perimeter of the shadow as it crossed over the Nevadan desert and measured the amount of time the star was obscured.

On October 20th, dozens of scientists spread out in a pattern to catch as much of the occultation as possible and to use their observational data to calculate the true size of Eurybates, which is one of the targets of the Lucy mission to the Trojan asteroids.  As with all science, it’s never as easy as it sounds.  

Another NASA Goddard video describing the target of the Lucy mission – the Trojan asteroids.
Credit – NASA Goddard

Despite taking place in a desert, clouds almost obscured the entire occultation, making it impossible to collect the data needed to find the true scope of the asteroid.  Just to make the calculations even more complicated, Hubble found a moon orbiting Eurybates that could confuse the data if it were not ideally positioned out of the way during the occultation.

Luckily the stars (and asteroids, and clouds) aligned, and the scientists were able to collect the data necessary to constrain the size of Eurybates better.  That updated estimate should also allow astronomers better to estimate the size of Lucy’s other targets.  This also won’t be the only occultation the Lucy team will observe – they’ll be traveling, most likely to much less hospitable places than Las Vegas, until Lucy’s last flyby of Patroclus, another Trojan asteroid, in 2033. 

UT video discussing the Lucy mission.

Learn More:
NASA – Watching the Blink of a Star to Size Up Asteroids for NASA’s Lucy Mission
Lucy – Eurybates Occultation 2021-10-20
Earth.com – Capturing the moment the asteroid Eurybates eclipsed a star

Lead Image:
Image of Earth with the occultation spot.
Credit – NASA Goddard

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