Author: Robert Zimmerman

A close-up of the dark side of Saturn’s moon Iapetus

11:55 am

Iapetus' equator ridge
Click for original image.

Cassini's first global close-up of Iapetus
Click for original image.

Today’s cool image is a double-header! The picture above, cropped to post here, was taken on September 10, 2007 during Cassini’s fly-by of Saturn’s moon Iapetus, taken from approximately 1,000 miles above the surface. It looks at the dark side of this two-toned planet (see yesterday’s cool image). As the moon’s rotation is tidally locked so that one side always faces Saturn, one hemisphere always leads while the other always trails. For some reason still unexplained, the leading hemisphere is covered with an almost pitch-black material, while the trailing hemisphere is bright and very white, its icy surface quite visible.

For context, to the right is a global image of that dark side taken during Cassini’s first fly-by of Iapetus on December 31, 2004. This picture highlights the long ridge that runs along the planet’s dark hemisphere’s equator that was the focus of the close-up image above. From the 2005 press release:

The most unique, and perhaps most remarkable feature discovered on Iapetus in Cassini images is a topographic ridge that coincides almost exactly with the geographic equator. The ridge is conspicuous in the picture as an approximately 12 miles band that extends from the western (left) side of the disc almost to the day/night boundary on the right. On the left horizon, the peak of the ridge reaches at least 8 miles above the surrounding terrain. Along the roughly 800-mile-length over which it can be traced in this picture, it remains almost exactly parallel to the equator within a couple of degrees. The physical origin of the ridge has yet to be explained. It is not yet clear whether the ridge is a mountain belt that has folded upward, or an extensional crack in the surface through which material from inside Iapetus erupted onto the surface and accumulated locally, forming the ridge.

Iapetus itself has a diameter of about 900 miles, so this ridge essentially crosses most of the dark hemisphere.

The 2007 press release did not provide enough information to pinpoint exactly where along that ridge the close-up is located, but no matter. Both images make very clear what we are looking at.

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China’s giant Spacesail constellation seeks more funding

9:57 am

Spacesail, one of the largest of China’s planned constellations designed to compete with Starlink, is now seeking more funding to build its full constellation of 10,000 to 14,000 satellites.

Shanghai Spacecom Satellite Technology, or SpaceSail, a satellite communications company developing a massive constellation known as “Qianfan,” disclosed plans to bring in new investors through a capital increase, according to a notice published on the Shanghai United Assets and Equity Exchange.

At present, this Chinese pseudo-company has launched only 119 out of the constellation’s first phase of 648 satellites. While it has gotten Airbus to sign a contract to use its constellation on its airplanes, it also appears to be somewhat cash poor, having only about $150 million on hand (much of it government funding), and is not going to meet its international licensing requirement to get those 648 satellites in orbit by the end of this year.

This new funding round announcement suggests it is in need of capital, and is having trouble getting the Chinese government to cough up the additional funds.

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Have astronomers spotted the collision of two exoplanets around a Sunlike star?

9:36 am

Changes in the infrared

Using data from a number of orbiting space telescopes, astronomers think they have detected the collision of two exoplanets, producing debris that for about 200 days variably blocked the light from the system’s star.

The images to the right come from figure 1 of their published paper [pdf], showing changes in the infrared as detected by the WISE space telescope. From the press release:

The star, named Gaia20ehk, was about 11,000 light-years from Earth near the constellation Pupis. It was a stable “main sequence” star, much like our sun, which meant that it should emit steady, predictable light. Yet this star began to flicker wildly. “The star’s light output was nice and flat, but starting in 2016 it had these three dips in brightness. And then, right around 2021, it went completely bonkers,” said Tzanidakis, a doctoral candidate in astronomy at the University of Washington. “I can’t emphasize enough that stars like our sun don’t do that. So when we saw this one, we were like ‘Hello, what’s going on here?’”

The cause of the flickering had nothing to do with the star itself: Huge quantities of rocks and dust — seemingly from out of nowhere — were passing in front of the distant star as the material orbited the system, patchily dimming the light that reached Earth. The likely source of all that debris was even more remarkable: a catastrophic collision between two planets.

…“The infrared light curve was the complete opposite of the visible light,” Tzanidakis said. “As the visible light began to flicker and dim, the infrared light spiked. Which could mean that the material blocking the star is hot — so hot that it’s glowing in the infrared.”

A cataclysmic collision between planets would certainly produce enough heat to explain the infrared energy. What’s more, the right kind of collision could also explain those initial dips in light.

The data suggests the collision occurred at an orbit comparable to that of the Earth’s, and took more than a half a year to largely dissipate.

All of this is a reasonable hypothesis based on the data available. Though there is a lot of uncertainty in this conclusion, the researchers considered other explanations, such as variability in the star itself, and found them less credible.

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FCC chairman blasts Amazon and its Leo satellite constellation

9:08 am

FCC logo

Brendan Carr, the chairman of the Federal Communications Commission, yesterday harshly criticized Amazon for filing papers opposing SpaceX’s application to place a million new satellites into orbit while failing to meet its own FCC license requirement to get 1,600 Amazon Leo satellites in orbit by July 2026.

Amazon should focus on the fact that it will fall roughly 1,000 satellites short of meeting its upcoming deployment milestone, rather than spending their time and resources filing petitions against companies that are putting thousands of satellites in orbit.

To put it mildly, Carr’s point is well taken. In legally protesting SpaceX’s proposed constellation while failing to launch on time as promised, Amazon is following what appears to be standard Jeff Bezos’ practice, epitomized by his rocket company Blue Origin. When customers begin favoring others because the Bezos company either submits a poor bid or fails to meet schedules, the Bezos companies routinely go to court in an attempt to squelch that better competition.

Carr is demanding Amazon stop this, and focus instead on getting its own job done for once. Carr is also signaling the FCC’s position on both SpaceX and Amazon. It is likely going to reject Amazon’s filing and give its okay to SpaceX’s million-satellite constellation, in one form or another.

Carr is also telling Amazon that it faces some push back for failing to launch the required number of Amazon Leo satellites on time. Though it is extremely unlikely the FCC will cancel Amazon’s Leo license, the FCC might fine it heavily. Or it could impose new limits on the constellation. Carr is also indicating the FCC will treat future Amazon license applications much more stringently.

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NASA’s Van Allen Probe A burns up over the Pacific

8:49 am

We didn’t all die! Van Allen Probe A, one of two NASA spacecraft launched in 2012 to study the Van Allen radiation belts that circle the Earth, yesterday burned up harmlessly over the Pacific ocean as expected.

Both Van Allen probes have been defunct since around 2019, when they ran out of fuel. Van Allen Probe B weighed about 1,300 pounds, so some pieces probably reached the ocean. Had it returned over land it did carry the small risk of doing harm.

The orbit of the other probe, Van Allen Probe B, is expected to decay sometime around 2030. Like its twin, it is heavy enough that some parts will survive re-entry. It is therefore a prime target for a demonstration mission proving the technology for removing space junk safely and under control. NASA should put out a request for bids to the many orbital tug companies that now exist to do exactly that, as it is NASA’s responsibility to make sure this spacecraft re-enters the atmosphere safely.

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Firefly launches its Alpha rocket, almost a year after previous launch failure

9:11 pm

Firefly today successfully launched its Alpha rocket, almost a year after a launch failure in April 2025.

This launch, from Firefly’s launchpad at Vandenberg Space Force Base in California, was the last for this version of Alpha, and was designed as a test flight, both to check out the fixes to correct last year’s failure as well as to prove out some of the technology that will be used on the upgraded Alpha to be used on all future flights.

The 2026 launch race:

30 SpaceX
8 China
3 Rocket Lab
2 Russia
1 ULA
1 Europe (Arianespace)
1 Firefly

SpaceX continues to lead the entire world combined in total launches — as it did in both ’24 and ’25 — and is doing almost twice as many launches as everyone else.

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Iapetus: Saturn’s ying-yang moon

11:55 am

Iapetus as seen by Cassini in 2007
Click for original image.

Cool image time! The image to the right, reduced and sharpened to post here, was taken on September 10, 2007 by the Saturn orbiter Cassini as it made its first close fly-by of the moon Iapetus, from a distance of about 45,000 miles.

Iapetus, about 912 miles in diameter, is one of the strangest objects in the solar system. As it orbits Saturn, its leading hemisphere is very dark, covered with almost pitch black material, while its trailing hemisphere is very bright. This picture captures a bit of both, with the dark leading hemisphere visible along the right edge.

In many places, the dark material–thought to be composed of nitrogen-bearing organic compounds called cyanides, hydrated minerals and other carbonaceous minerals–appears to coat equator-facing slopes and crater floors. The distribution of this material and variations in the color of the bright material across the trailing hemisphere will be crucial clues to understanding the origin of Iapetus’ peculiar bright-dark dual personality.

There are several theories to explain the planet’s strange ying-yang two-tone coloration. One suggests it is material thrown off by other Saturn moons that Iapetus sweeps up. Other theories suggest the planet’s orbit itself causes the two hemispheres to have different temperatures, allowing material to sublimate off the dark side and to the bright side.

No theory is presently accepted. Nor does any explain the data fully.

Tomorrow I’ll post a most intriguing close-up of Iapetus taken by Cassini during that 2007 fly-by.

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Interstellar comet 3I/Atlas is unusually enriched with windshield wiper fluid

10:45 am

New Hubble image of 3I/Atlas
Comet 3I/Atlas as seen by Hubble
in November 2025. Click for original.

While interstellar comet 3I/Atlas is remarkably like most comets from our own solar system, scientists have now found new evidence that it spalled off unusual amounts of methanol (CH3OH) — material normally used as windshield washer fluid, carburetor fluid, and cooking fuel — when it made its close fly-by of the Sun in the fall of 2025.

You can read the paper here [pdf] . The research also detected large amounts of prussic acid (HCN). As the comet made its closest pass to the Sun, the numbers increased. From the paper’s abstract:

The CH3OH production rate increased sharply from August through October, including an uptick near the inner edge of the H2 O sublimation zone at r H = 2 au. Compared to comets measured to date at radio wavelengths, the derived CH3 OH/HCN ratios in 3I/ATLAS of 124+30 −34 and 79−14 +11 on September 12 and 15, respectively, are among the most enriched values measured in any comet, surpassed only by anomalous solar system comet C/2016 R2 (PanSTARRS).

Though the numbers are high, they aren’t outside the range of what has been found in comets from our own solar system. Instead, this data suggests — as has all data so far — that Comet 3I/Atlas is a normal comet, but unique in its own way, as are all comets and in fact every object in space.

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Fourteen-year-old NASA satellite about to burn up uncontrolled in the atmosphere

9:27 am

Chicken LIttle rules again.

Chicken Little rules again! After fourteen years, the orbit of one of NASA’s two Van Allen Probe satellites is about to decay, causing the 1,323 pound satellite to burn up uncontrolled in the atmosphere.

As of March 9, 2026, the U.S. Space Force predicted that the roughly 1,323-pound spacecraft will re-enter the atmosphere at approximately 7:45 p.m. EDT on March 10, 2026, with an uncertainty of +/- 24 hours. NASA expects most of the spacecraft to burn up as it travels through the atmosphere, but some components are expected to survive re-entry. The risk of harm coming to anyone on Earth is low — approximately 1 in 4,200.

As today is a very slow news day in space news, a lot of the mainstream press is highlighting this story, with the usual fear-mongering about how it could hit the Earth and cause terrible damage. And while it is certainly true that this satellite appears large enough for some pieces to reach the ground, the chances of those pieces causing any real harm is quite slim. In fact, I think NASA’s estimate of 1 in 4,200 to be far too high.

Mission engineers had initially estimated the orbit would decay in the 2030s, but that estimate was based on a prediction of a weak solar maximum. The Sun however was more active than predicted in the past decade, and that activity caused the Earth’s atmosphere to puff up, which in turn acted to accelerate the satellite’s orbital decay.

This incident once again shows us that there is money to be made in removing defunct satellites from orbit. NASA and ESA have both made it clear each would pay a company to do it. So have some private companies. Some of the orbital tug and robotic servicing companies have here an opportunity they need to grab.

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