After DART Smashed Into Dimorphous, What Happened to the Larger Asteroid Didymos?
NASA’s DART mission (Double Asteroid Redirection Test) slammed into asteroid Dimorphos in September 2022, changing its orbital period. Ground and space-based telescopes turned to watch the event unfold, not only to study what happened to the asteroid, but also to help inform planetary defense efforts that might one day be needed to mitigate potential collisions with our planet.
Astronomers have continued to observe and study Dimorphos, well past the impact event. However, Dimorphos is the smaller asteroid in this binary system, and is just a small moon orbiting the larger asteroid Didymos.
The James Webb Space Telescope (JWST) is the only telescope capable of visually distinguishing between the two closely orbiting asteroids. Now, astronomers have made follow-on observations on the system with JWST to see what happened to Didymos after the dust cleared.
In a new preprint paper, a team of scientists, led by Andrew Rivkin, the Investigation Lead for DART, explain how they used two instruments on JWST to measure spectra of Didymos about two months after the DART impact. One of their biggest takeaways is that Didymos and Dimorphos appear to be of the same composition, which is that of an ordinary chondrite. That’s the class of stony meteorites which account for over 80% of total meteorite falls on Earth. This means DART’s test was an extremely good proxy for the type of asteroids that might pose a threat one day.
“One of the benefits of using the Didymos system was definitely that we thought it was representative of most of what’s out there in its properties,” Rivkin told Universe Today via email. “People working on planetary defense often note that the ‘asteroid picks us rather than the other way around,’ but showing that what we did at Dimorphos is broadly applicable is very important.”
For the new observations, the scientists used NIRSpec – the near infrared spectrometer — and MIRI, the mid-infrared instrument, on November 28, 2022.
At the time of the observations, the centers of Didymos and Dimorphos were never separated by more than 0.1” from each other, from JWST’s vantage point. But the team did take advantage of Dimorphos being occulted by Didymos during the MIRI observations.
Median averaged slice through the MIRI MRS IFU showing Didymos. Note that Dimorphos was being occulted by Didymos during the entire period of MIRI observations.Credit: Rivkin et al, 2023.
“Didymos is roughly five times larger in diameter than Dimorphos and therefore it has roughly 25 times the cross-sectional area as Dimorphos,” the researchers wrote. “This size difference between the components means that roughly 96% of flux from the system typically comes from Didymos.”
The researchers said several lines of evidence suggest that the asteroid and its moon have similar compositions and the team concludes they “can reasonably estimate the composition of Dimorphos specifically from measurements of the Didymos-dominated flux.”
This image from the DART spacecraft of the light from asteroid Didymos and its orbiting moonlet Dimorphos. Credit: NASA/JPL-Caltech/DART Navigation Team
Given how hard it is to distinguish between Didymos and Dimorphos in long-range observations, I asked Rivkin if they were able to see any noticeable changes in the observations of Didymos after the impact to Dimorphos, given all
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How to Get a Permit to Backpack the Teton Crest Trail
backpackers, the Teton Crest Trail really delivers it all: beautiful lakes,
creeks, and waterfalls, high passes with sweeping vistas, endless meadows of
vibrant wildflowers, a good chance of seeing wildlife like elk and moose, some
of the best campsites you will ever pitch a tent in, and mind-boggling scenery
just about every step of the way. And it’s a relatively beginner-friendly trip
of 40 miles or less, which most people can hike in four to five days.
No wonder it’s so enormously popular—and there’s so much competition for backcountry permits.
In this story, I will offer tips on how to maximize your chances of getting a permit to backpack the Teton Crest Trail, sharing expertise I’ve acquired from more than 20 trips in the Tetons and several on the Teton Crest Trail over more than three decades, including the 10 years I spent as Northwest Editor of Backpacker magazine and even longer running this blog.
Hi, I’m Michael Lanza, creator of The Big Outside. Click here to sign up for my FREE email newsletter. Join The Big Outside to get full access to all of my blog’s stories. Click here for my e-guides to classic backpacking trips. Click here to learn how I can help you plan your next trip.
Lake Solitude, North Fork Cascade Canyon, Grand Teton National Park.
” data-image-caption=”Lake Solitude in the North Fork of Cascade Canyon, Grand Teton National Park. Click photo for my e-guide “The Complete Guide to Backpacking the Teton Crest Trail.”
” data-medium-file=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?fit=300%2C200&ssl=1″ data-large-file=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?fit=900%2C600&ssl=1″ src=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?resize=900%2C600&ssl=1″ alt=”Lake Solitude, North Fork Cascade Canyon, Grand Teton National Park.” class=”wp-image-36414″ srcset=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?resize=1024%2C683&ssl=1 1024w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?resize=300%2C200&ssl=1 300w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?resize=768%2C512&ssl=1 768w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?resize=1080%2C720&ssl=1 1080w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?w=1200&ssl=1 1200w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />Lake Solitude in the North Fork of Cascade Canyon, Grand Teton National Park. Click photo for my e-guide “The Complete Guide to Backpacking the Teton Crest Trail.”
See my story from my most-recent trip on it, “A Wonderful Obsession: Backpacking the Teton Crest Trail,” which requires a paid subscription to The Big Outside to read in full, including basic information on planning a TCT backpacking trip. For much more information and expert tips on planning this trip, get my top-selling e-guide “The Complete Guide to Backpacking the Teton Crest Trail in Grand Teton National Park.”
I’ve also helped many readers plan a backpacking trip in the Tetons and elsewhere, answering all of their questions and customizing an itinerary ideal for them. See my Custom Trip Planning page to learn how
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Eris Could be Slushier Than Pluto
In 2005, astronomer Mike Brown and his colleagues Chad Trujillo and David Rabinowitz announced the discovery of a previously unknown planetoid in the Kuiper Belt beyond Neptune’s orbit. The team named this object Eris after the Greek personification of strife and discord, which was assigned by the IAU a year later. Along with Haumea and Makemake, which they similarly observed in 2004 and 2005 (respectively), this object led to the “Great Planet Debate,” which continues to this day. Meanwhile, astronomers have continued to study the Trans-Neptunian region to learn more about these objects.
While subsequent observations have allowed astronomers to get a better idea of Eris’ size and mass, there are many unresolved questions about the structure of this “dwarf planet” and how it compares to Pluto. In a recent study, Mike Brown and University of California Santa Cruz professor Francis Nimmo presented a series of models based on new mass estimates for Eris’ moon Dysnomia. According to their results, Eris is likely differentiated into a convecting icy shell and rocky core, which sets it apart from Pluto’s conductive shell.
Their paper, “The internal structure of Eris inferred from its spin and orbit evolution,” recently appeared in the journal Science Advances. The research began while Nimmo was visiting Professor Brown at Caltech and realized that some of his previously-unpublished data could help reveal information about the properties of Eris. At present, we know that Eris is about the same size and mass as Pluto and has a highly eccentric orbit around our Sun, ranging from 38.271 AU at perihelion to 97.457 AU at aphelion. This is almost twice as eccentric as Pluto’s orbit and roughly 50% farther from the Sun.
Comparison between the eight largest TNOs with Earth (all to scale). Credit: NASA/Lexicon
For several months, Brown and Nimmo worked on models of Eris that incorporated two key pieces of information. The first had to do with Eris’ only known satellite, Dysnomia, and how the two bodies always face the same way toward each other. “That happens because the big planet gets spun down by the tides that the little moon raises on it,” said Nimmo in a recent UCSC press release. “The bigger the moon is, the faster the planet spins down. And so as soon as you know that, then you can actually start to do real calculations.”
Astronomers can use the spin and orbital characteristics of planets and their moons to infer certain properties, like their internal structures. But until recently, scientists did not have estimates on Dysnomia’s size, mass, and density. Luckily, Brown and his colleague Bryan J. Butler – a researcher at the National Radio Astronomy Observatory (NRAO) – recently conducted observations of Dysnomia and Eris (and Orcus and its satellite Vanth) using the Atacama Large Millimeter-submillimeter Array (ALMA). Based on their findings, published in The Planetary Science Journal, Dysnomia has a diameter of about 615 km (382 mi) and Dysnomia and Eris have a mass ratio of 0.0085.
This upper mass limit provided the second crucial piece of information, which concerned Eris’ internal structure. The main result of Brown and Nimmo’s model (but did not expect) is that Eris is surprisingly dissipative, a concept in thermodynamics where a system operates out of equilibrium. From this, they determined that Eris has a rocky core surrounded by a layer of ice and a crust that is likely convecting. “The rock contains radioactive elements, and those produce heat,” Nimmo said. “And then that heat has to get out somehow. So as the heat escapes, it drives this slow churning in the ice.”
This sets it apart from Pluto, which has a conducting shell, as revealed by the New Horizon mission. Brown and Nimmo hope that more exact measurements of Dysnomia’s mass will be available in the near future, as well as additional data about the shape of Eris. Because of its distance, Eris appears as a single pixel of light, while Dysnomia is visible as a faint speck next to it (see below). Therefore, astronomers must monitor Eris as it passes in front of background stars to reconstruct its shape. This is similar to the Transit Method astronomers use to detect exoplanets and constrain their sizes.
Hubble is Offline Because of a Problem with one of its Gyros
The rich flow of scientific data—and stunning images—that comes from the Hubble Space Telescope is being interrupted by gyro problems. One of the telescope’s three remaining gyros gave faulty readings, and the Hubble automatically entered safe mode. In safe mode, science operations are suspended.
Without gyros, the Hubble can’t orient itself properly. Gyros measure the telescope’s turn rate and help the telescope know where it’s pointed. They’re part of the system that keeps the space telescope pointed in the right direction. There’s no indication of any problems with Hubble’s instruments, like its Wide-Field Camera 3 or its Advanced Camera for Surveys.
This all began on November 19th when Hubble went into safe mode. Engineers recovered the telescope, and regular science operations resumed the following day. However, the unstable gyro caused problems again, and the space telescope suspended science operations again on the 21st. It was recovered again, then went back into safe mode on November 23rd. That’s where things stand now.
NASA is working to resume science operations of the Hubble Space Telescope after it entered safe mode Nov. 23 due to an ongoing gyroscope issue. Hubble’s instruments are stable, and the telescope is in good health: https://t.co/QOdJJ9WjYh pic.twitter.com/URRHYV3Le8
— Hubble (@NASAHubble) November 29, 2023
The Hubble was launched with six original gyros, but they failed fairly rapidly. During its last shuttle servicing mission in 2009, the Hubble received six new gyros. Three of them were the older type that failed fairly quickly, and three were new ones. The three older ones from 2009 have failed, and Hubble has three remaining gyros, and all of them have a more modern design. It can operate with a single functioning gyro, though it’s less efficient.
This image shows astronaut Mike Massimino during Service Mission 4 to the Hubble in 2009. Astronaut Mike Good is in the background. During SM-4, Hubble received new gyroscopes, as well as two new scientific instruments – the Cosmic Origins Spectrograph (COS) and Wide Field Camera 3 (WFC3). Image Credit: NASA
Each gyro is a small cylinder filled with fluid. Inside the fluid, an internal float spins thousands of times per second. The original six gyros and three of the 2009 replacements contained bromine in the fluid. The bromine ate away at the gyros, causing their eventual demise.
One of the Hubble’s gyros. Older ones had bromine in their interior fluid, which ate away at the gyros, causing their demise. Image Credit: NASA
This isn’t the first time failing gyros have caused a shutdown in Hubble’s science operations. The preceding incident happened in 2018. At that time, Ken Sembach was the Director of the Space Telescope Science Institute (STScI.) In an interview, he expressed some frustration, telling Business Insider, “We’ve had some issues with this gyro in the past, and we’ve got some possible leads on the current problem. But the thing that’s been clear on Hubble is that these gyros all have a mind of their own. I don’t think anybody really knows what’s going on with it right now.”
The gyros are just part of the system that keeps Hubble pointed where astronomers want it pointed. The system also includes reaction wheels and fine guidance sensors
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