Comet Confusion and the Psyche Mission’s Mars Encounter

[00:00:00] This is Space Time, Series 29, Episode 91, for broadcast on the 31st of July, 2026. Coming up on Space Time, the near-Earth asteroid that turned out to be a comet, NASA's Psyche spacecraft's gravity assist flyby of Mars, and China's about to double the size of its space station. All that and more coming up on Space Time. Welcome to Space Time with Stuart Gary.

[00:00:45] Astronomers have confirmed that the near-Earth asteroid 1998 SH2 is actually a comet, further blurring the lines between these two different types of celestial bodies. The problem was, the object originally looked like a typical asteroid in most telescope images, showing none of the usual comet-like characteristics, such as degassing a fuzzy coma nucleus and cometary tails. But the unusual thing was, this asteroid was on a comet-like orbit.

[00:01:12] The new findings, reported in the journal Nature Astronomy, are based on fresh, more detailed observations. The puzzle began back on August 28, 2025, when 1998 SH2 passed within 3 million kilometres of the Earth during its 4.5-year orbit around the Sun. Astronomers took the opportunity to observe the asteroid with NASA's Deep Space Network Planetary Radar System. They had calculated its position using data from previous orbits,

[00:01:39] and factored in the effects that the gravity of the Sun and planets would have had on its path. But when the asteroid didn't show up where they expected, they realized that something unanticipated must have been influencing its motion through space. By using optical astrometry to precisely measure the object's position in the sky, they were finally able to identify the cause. The study's lead author, David Fenochia from NASA's Jet Propulsion Laboratory in Pasadena, California,

[00:02:05] says that after measuring the non-gravitational perturbations affecting the motion of 1998 SH2, his team recognized that they weren't compatible with the object being an asteroid, and began to suspect that it may well be an active comet instead. Although 1998 SH2's orbit around the Sun has been world-tracked from 1998 to 2016, the object had completed two solar orbits since then without any additional observations.

[00:02:30] Analyzing all the observations collected since the object's discovery back in 1998, the authors determined the perturbations to 1998 SH2's motion and hypothesized that the object must be generating a small amount of its own thrust, possibly by venting gases into space. And that was what was causing it to deviate from its projected path. Now this venting results from the Sun heating ices mixed with rocky material turning the ice into a gas.

[00:02:57] With regular comets, this activity forms the trademark bright tail and coma, that's the gas and dust surrounding the comet's nucleus. But when an object produces its gas and dust in much smaller quantities, its tail and coma may not be detectable by most observatories. So, the August 2025 close approach to Earth provided the perfect opportunity for Fenochia and colleagues to gather observational evidence for any possible visible cometary activity.

[00:03:24] They used the Canada-France-Hawaii telescope at Mauna Kea, as well as the European Southern Observatory's Danish telescope at La Silla, and its VLT or Very Large Telescope at Paranal, both in Chile, to study this object in more detail, in the process revealing a weak but clear cometary tail. As a result, 1998-SH2 has now been given an additional cometary designation, P1998-SH2.

[00:03:50] The findings also shed light on another, even more unusual class of objects, known as dark comets. Like P1998-SH2, dark comets exhibit significant irregularities or perturbations in their trajectories. But they lack other visible evidence of comet-like activity. There's no coma, no tail, and no visible outgassing. These distinct objects fall into two distinct populations. Larger ones with orbits similar to those of Jupiter family comets,

[00:04:19] these are short-period comets with highly elliptical or eccentric orbits, and smaller comets that orbit closer into the Sun. Since the 2016 discovery of the first dark comet, there are a dozen more have been identified. The authors suggest that many of the larger dark comets, which have orbits like P1998-SH2s, could turn out to be regular comets. That's if astronomers can get the opportunity to observe them with more powerful telescopes, once capable of imaging incredibly faint objects. Fanatius says,

[00:04:48] The work shows the importance of continuously tracking near-Earth objects. Detecting these perturbations would be an important diagnostic tool for planetary defense that will help astronomers understand which objects may be comets rather than asteroids, how their orbits evolve, and how that could influence their chances of impacting the Earth. This is Space Time. Still to come, NASA's Psyche spacecraft undertakes a successful gravity-assist flyby of the red planet Mars,

[00:05:17] and as NASA prepares to wind down and deorbit the International Space Station, China announces plans to double the size of its own space station. All that and more still to come, on Space Time. This episode of Space Time is brought to you by NordVPN, Space Time's official VPN service. Let's face it, these days your online privacy is more important than ever. Whether you're streaming science documentaries, reading the latest research, or exploring deep space images,

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[00:07:15] has undertaken a successful gravity assist flyby of the red planet Mars, a manoeuvre which will help slingshot the probe towards ultimate target, the strange metallic asteroid 16 Psyche. The 226-kilometre-wide metal-rich asteroid orbits the Sun in the main asteroid belt between Mars and Jupiter. It contains about 1% of the entire mass of the main asteroid belt, and is primarily composed of iron, nickel, and precious metals, giving it a hypothetical mining valuation

[00:07:44] exceeding 10 quintillion US dollars. Saki was originally chosen for the mission because it was thought to be the exposed metallic core of a larger differentiated planetary body, which had its metal and crust stripped away during some sort of ancient impact event. And that made Saki a prime target for astronomers wanting to study the internal structures of planets. However, as they began getting more and more data on the asteroid, they received mass and density observations

[00:08:12] that were inconsistent with Saki being a remnant planetary core. That led to a new hypothesis, suggesting that Saki had been disrupted and then gravitationally re-accreted into a mix of metal and silicates. That would make it a potential parent body for the meso-satirites class of stony iron meteorites. Another hypothesis suggests that Saki may be a differentiated object like Ceres and Vesta, but one that experienced a type of iron volcanism

[00:08:39] called ferrovolcanism while still cooling. Now, if correct, this model predicts that metal would be highly enriched only in those regions containing relic volcanic centers, a view supported by recent radar observations. Meanwhile, by this time, the Saki spacecraft had already launched on its mission. It aced its close encounter with Mars, using the planet's gravity to gain speed and slightly tilting its trajectory. The flyby also gave mission managers an opportunity to prep for the science they'll be conducting

[00:09:08] when they finally reach the middle-rich asteroid Saki in 2029. They tested the spacecraft science instruments, confirming all were operating nominally, providing data that matched what NASA already knew about Mars, and also providing a few new insights about the red planet along the way. Saki's principal investigator, Lindy Elkins-Tanton, from the University of California, Berkeley, says the spacecraft's imager, magnetometer, and gamma ray and neutron spectrometer teams all worked overtime

[00:09:36] to make full use of the planetary encounter, and all instruments delivered great results. The gamma ray and neutron spectrometer, which helped scientists determine the chemical elements that make up the asteroid's surface material, got a real workout during the flyby. As high-energy cosmic rays bombarded Mars, elements on the red planet's surface absorb energy, emitting neutrons and gamma rays of varying energy levels. By measuring these emissions, scientists can match them the properties of known elements in order to determine what the body's made of.

[00:10:06] While the Mars flyby altitude of 4,609 kilometers was too far away to measure gamma rays, neutrons escaping the planet's surface and atmosphere could be detected. The mission's magnetometer is designed to measure Saki's magnetic field, and it was designed to test the idea that it could be the metallic core of a planetesimal, the building block of a rocky planet. While this instrument's been constantly measuring the solar wind's magnetic field throughout its cruise phase, including when occasional coronal mass ejections washed over the spacecraft,

[00:10:35] Mars was the first magnetic field signature of a celestial body that the magnetometer was able to measure. As the spacecraft passed close to the red planet, the magnetometer saw an increased uptick in magnetic field corresponding to the bow shock region, where the solar wind slams into the planet's magnetic field. Meanwhile, the spacecraft's multi-spectral imager, a pair of identical cameras designed to photograph the surface of the asteroid in different wavelengths, delivered some stunning views of Mars during the flyby. Because of the high phase angle

[00:11:05] at which the spacecraft approached the red planet, Mars initially appeared as nothing more than a thin, bright crescent with sunlight scattering through its atmosphere. During close approach, the imager team captured detailed views of the Martian surface, including wind-blown craters, the South Polar Ice Cap, the large double-ringed Huygens crater, and the two Martian moons, Phobos and Deimos. Psyche project manager Bob Mays from NASA's Jet Propulsion Laboratory in Pasadena, California, says the Psyche spacecraft

[00:11:34] remains in great shape and is now headed directly towards its ultimate target. He says the probe's on schedule to resume sustained thrusting using its solar electric propulsion system in a couple of months' time. This report from NASA TV. For a fleeting moment on May 15, 2026, NASA's Psyche spacecraft drew close enough to Mars to see its craters, calibrate its instruments, and then it kept going.

[00:12:02] Coming within 2,864 miles of the red planet's surface, the Psyche mission got a critical gravity assist on its way toward the metal-rich asteroid Psyche. Analyzing radio signals between the spacecraft and NASA's deep space network, Psyche's flight team confirmed Mars gave the spacecraft a 1,000-mile-per-hour boost and shifted its orbital plane relative to the sun by more than 3 degrees, setting it almost perfectly on its planned trajectory to arrive at asteroid Psyche

[00:12:30] in the summer of 2029. During the flyby, Psyche's imagers, magnetometer, and gamma-ray and neutron spectrometer instruments were powered up and collected data to take advantage of the valuable calibration opportunity the close approach offered, comparing its measurements to surface and atmospheric data from several other Mars missions. Psyche's spectrometer measured neutrons coming from the red planet's surface during close approach, something it will do at asteroid Psyche to better understand

[00:13:00] what it's made of. The magnetometer detected Mars' magnetic field interacting with the sun's plasma as the spacecraft passed through the planet's bow shock, a trial run for when the instrument will measure the asteroid's magnetism, and Psyche's multispectral imager was especially active. An event like this takes a ton of planning. We like to use a system called Cosmographia to simulate everything in advance. You know, how close do we need those images to be as we pass really close to Mars in order to see enough of an overlap

[00:13:30] that we can make a huge mosaic out of it. It gives us a beautiful opportunity to see the big picture and to really put it all together. As a bonus, Psyche's multispectral imager captured Mars from a rare perspective. Coming in at such a high phase crescent, only 4% of Mars was illuminated, and with that, we could see the atmosphere around it glowing. So you could see clouds on Mars. It was really quiet as the three of us just kind of sat back there looking at it. My favorite image is the one

[00:13:59] that looks like an eye, and I love how it starts with Mars as a really tiny little crescent, and then every day it gets slightly bigger and slightly bigger until we have 14 images stacked up. So it gives us a nice perspective on the speed the spacecraft is traveling at. The detail that we were able to see in some of these terrain, I personally was blown away. The southern polar cap, Huygens crater, I think the windstreaked terrain was really interesting. It shows like active

[00:14:27] processes happening on Mars. It was very exciting to be able to finally put the whole thing together and then see Mars getting bigger and then smaller in the field of view again. Feels great to finally have more to share with the world. With Mars behind Psyche, the spacecraft will soon resume thrusting with its solar electric propulsion system. Next stop, the asteroid belt onward to Psyche. And in that report from NASA TV, we heard from Psyche Multispectral Imager Operations Team members Nicole Gonzalez and Hannah Zygo,

[00:14:57] both from Arizona State University. This is Space Time. Still to come, China about to double the size of its space station and later in the science report, new clues about how the human body's nervous system senses warm and cool temperatures. All that and more still to come on Space Time.

[00:15:31] As NASA looks at winding down and de-orbiting the International Space Station in 2030, Beijing has announced plans to double the size of its Tiangong space station. The expansion will see the orbiting armost transform from its existing three modules to six, in the process changing its layout from a T-shape to a sort of cross or double T. Included in the expansion will be a new 20-ton class multifunctional hub featuring six docking ports and an extra vehicle activity hatch for spacewalks

[00:16:00] as well as two new modules also in the 20-ton class, all of which will combine to allow China to dramatically expand its operations. The changes will also increase the station's mass from 77 tons somewhere between 180 and 200 tons and it will allow the station's permanent crew capacity to grow from the current three up to at least six Tarkinauts at a time. The plans also include launching the new Hubble-class Juneteen space telescope which will fly in formation with the space station

[00:16:29] and occasionally dock with it for maintenance refuelling and repairs as well as potential upgrades. The new telescope will feature a 2-metre primary mirror and it's slightly smaller than the 2.4-metre mirror used on Hubble and it will use a 2.5 billion pixel camera. Juneteen is scheduled for launch next year and is expected to have at least a 10-year lifespan. The first modules of Tiangong, Mandarin for Heavenly Palace were launched back in 2021 with crews of three Shenzhou Taikonauts serving on station

[00:16:59] at any given time. China is also developing new cargo ships to resupply the space station and it's been developing its new seven-man Mengzhu spacecraft which will ultimately replace the current Russian-based three-man Shenzhou capsule. This is Space Time.

[00:17:18] And time now

[00:17:47] to take another brief look at some of the other stories making news insights this week with a science report. New researchers challenged what scientists understand about how the body's central nervous system senses warm and cool temperatures. Scientists at the University of Queensland have found that most of the skin's temperature-sensitive nerve cells can sense both hot and cold. The findings reported in the journal Neuron challenges the widely accepted view that the skin relies on separate nerve cells to detect each type of temperature.

[00:18:18] A new study based in the Western Australian Wheatbelt has found alarming levels of pesticide contamination in the food sources of endangered carnivores cockatoos near seed spills and grain silos. Over three breeding seasons wild carnivores were fitted with satellite tracking tags across five Wheatbelt a breeding site in order to identify where and what they were eating. A report in the journal Environmental Toxicology and Pharmacology claimed seed samples were then tested for pesticide contamination

[00:18:47] and the results showed concentrations well above regulatory limits. Scientists have found evidence of an ancient species of snake that lived almost exclusively underground. A report in the journal Nature claims the species Temeteria miriam a newly identified extinct snake species found in Brazil which lived around 85 to 75 million years ago was adapted for life underground. That's in contrast to other early snake species that lived above the ground or in water. The authors say the newly

[00:19:17] discovered fossil includes a well preserved three dimensional skull and body and is the first known articulated snake fossil found in Brazil. X-rays of the remains show its skull was shaped for burrowing and its brain was quite different from that of other snakes both extinct and living. And this suggests snake evolution was far more dynamic than previously thought. A new study warns that working from home may not have a significant impact on your carbon footprint. A report in the journal Plus Climate

[00:19:47] claims the emissions saved by not commuting are largely all offset by running a home office. The authors found that working more days from home and having a separate home office were both linked to higher overall emissions. And it wouldn't be Friday without a Bigfoot story and there's been a spate of eight Bigfoot sightings over a period of just five days in the American state of Ohio. The skeptics Tim Mendham says the sightings all occurred in the state's northeast but they appear to have involved

[00:20:17] very different looking Sasquatches. Seen eight times in one week in Ohio in a small area of Ohio and Trumbull County and this has been seen from people saying I saw it at a distance of about 120 yards or so when it was at 100 metres nine foot tall brown head sat what in the middle of the day broad daylight they saw it and then it ran off another person said the hiker said they spotted an eight foot tall creature with dark brown hair sitting out from behind trees just 40 yards away and this one actually yelled about a deep echoing grunt

[00:20:46] a terrified ex-veteran I don't know what actually being an ex-veteran relevance is but obviously ex-military described feeling watched and hearing this hellish roar that left him scared obviously he didn't see a Sasquatch or a big foot and I mean a lot of sightings within a short period of time five days and I assume that these got publicity at the time so you would suspect that some people were inspired were pre-prepared or something you know to actually see something that if they saw something strange they think it's a big foot the dogs apparently get very upset shaking with fear no definitive proof no photos

[00:21:16] they found a couple of footprints but often if you see big footprints they're not very convincing necessarily there could be a lot of things a lot of interpretation goes into these evidence and I've seen footprints of supposed of Australia the Yowie and just kidding really yeah they don't look like foots very strong correlation between an increase in Sasquatch sightings and an increase in bear populations yes or deer maybe there's the Sasquatch there maybe there really is it'd be fascinating to see I think we'd all like to see something like that it'd be very exciting but as for proof of it

[00:21:46] a lot of sightings in one short time is exciting but not necessarily definitive proof what I always say is that a bit of evidence which rates two out of ten because you don't have any other evidence that's just anecdotal is interesting eight bits of evidence that rate two out of ten do not give you a ten out of ten they give you a lot of two out of ten right and in fact the more two out of tens you get the less likely something is to be true because you say we've only got bad evidence you haven't got good evidence we've got a lot of bad evidence we've got a lot of apparently these

[00:22:15] people didn't including the ex-veteran it's a thing that people say it's happening all the time yeah but it's happening badly all the time it's not happening convincingly all the time and the more non-convincing it is to me the less likely it is to be true that's the skeptics Tim Mindham and this is Space Time

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