Mars Pathfinder: What Really Happened?

October 11, 2026 by Al Williams 33 Comments

You’ve probably heard of Mars Pathfinder, the NASA lander and its Sojourner rover that took up residence on Mars in 1997. At first, all was well, but after a few days, the lander suffered a series of total system resets. A watchdog timer detected a problem and forced reboots. [Vivek Bhageria’s] recent post looks into what happened and the eventual solution.

The root cause was priority inversion. This happens when a lower-priority task holds a resource needed by a higher-priority task and prevents the higher-priority task from executing. In this case, the operating system was VxWorks, but this can happen on any kind of priority scheduling system.

The simplified version is that there were two tasks that each used the same mutex to avoid stepping on each other. The highest priority was a data distribution task. The lowest priority task dealt with meteorology data processing. There was also a medium-priority task that handled bus maintenance.

The failure would occur when the low-priority task had the mutex and lost its time slot before releasing it. The high-priority task would then find it couldn’t take the mutex. However, the low-priority task didn’t get control again because of the medium-priority tasks waiting to run.

In effect, the high-priority task was now waiting on something that couldn’t become available until the lowest-priority task was able to run. That’s priority inversion.

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Scientists Create Hexagonal Packed Ice At Extreme Pressures

October 6, 2026 by Maya Posch 10 Comments

One of the problems with planetary science is that you generally cannot easily investigate the exact conditions in their interior, so you’re left to extrapolate what is happening inside them based on surface scans. One of the resulting questions is what ice giants like Neptune and Uranus in Earth’s solar system have exactly at their core. We do know that it is mostly rocks and ice, but what kind of ice you end up with at these intense pressures is a good question that [Alexis Forestier] et al. set out to answer, with their results published in a Physical Review Letter paper (ArXiv preprint).

It’s noteworthy that there isn’t just water ice at these planetary cores, with this study only investigating water ice specifically. In order to get the water to the pressures it would experience courtesy of ice giant gravity, a diamond anvil was used, with synchrotron x-ray diffraction allowing for the changes to the sample to be observed.

The phase diagram of water includes a number of phases beyond what us Earth-dwellers would call ‘ice’, with at higher pressures above about 80 GPa the formation of ice X, featuring a body-centered cubic (BCC) oxygen sublattice. Subsequent discovered phases were face-centered cubic (FCC) and now hexagonal close-packed (HCP) ice, all differing in the packing of the oxygen sublattice.

In addition to extreme pressures, temperatures also had to be increased by using the laser heating feature of the diamond anvil. At around 2,000K and over 200 GPa the HCP phase was found, with a mixed FCC-HCP phase at intermediate pressures.

Although not immediately providing answers to questions pertaining to the aforementioned ice giants, it gives planetary scientists yet another clue that they can use in future investigations, as well as provide more insight into this most fascinating phase of water that’s actually its own little galaxy of phases.

The Big Moon Plot

October 4, 2026 by Ian Bos 3 Comments

When you look into the night sky, you can’t help but wish to bring the outer worlds to your doorstep. One of the best ways to do that is to photograph the Moon’s surface to display in a frame. However, [Sebastian Lague] found a simple image too lackluster compared to something with a bit more style, such as a plotted image of the lunar terrain.

Why plotting? Well, the Moon is not defined in the same way with contrasting colors as Earth is. The Moon is peppered with craters and differing elevations that separate regions, so why not build an entire DIY plotter from scratch? [Sebastian Lague] did exactly this with a custom algorithm to take the elevation maps and create vector drawings which are plotted on his custom plotter.

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That’s No Moon… That’s An Exoplanet!

October 3, 2026 by Al Williams 6 Comments

It wasn’t that long ago that a science teacher would have told students that there was no evidence of planets around other star systems. Even more recently, they might have said that while we’ve seen evidence of extra-solar planets, we would never be able to see them directly. But that’s all changed. [Jason Wang] has several videos that use images taken over years to visualize the orbit of several large exoplanets.

Of course, some extrapolation is involved. According to [Jason]:

We unfortunately do not have the luxury of watching these planets every night and record them. However, these planets move slowly, with orbital periods at least decades long, and predictably following Kepler’s laws. We can use a technique called motion interpolation to reconstruct what the image should look like using images taken before and after the date we are interested in. Motion interpolation is a technique commonly found in video editing and in modern TVs.

You have to be a patient photographer, apparently. One video has 30 images taken over 17 years, for example. Another has 10 images from the Keck Observatory taken over 12 years.

The work has fed scientific papers like this one or this one. While it might be more fun to see these star systems from the bridge of your favorite starship, this is probably as close as you are going to get.

We find both the prospect of exoplanets and the technology used to find them exciting

Roman Telescope Saves Fuel, Doubles Mission

September 30, 2026 by Zoe Skyforest 18 Comments

Contemplate the events that might end a space mission, and you might picture something dramatic: detonation on the pad, a dead guidance system, or micrometeoroids shattering delicate solar panels. More often, though, the ending is far more mundane. Plenty of perfectly healthy spacecraft have been retired simply because the fuel tanks ran dry. That’s why mission planners guard every kilogram of go juice so jealously, and why careful preparation in a mission is critical to long-term success.

Which brings us to NASA’s Nancy Grace Roman Space Telescope. Barely two weeks after its August 30 launch on a Falcon Heavy, the mission team announced that Roman now has enough fuel for at least 22 years of science operations. That’s well over double its original 10-year fuel budget. It’s a huge gain, so let’s explore how NASA pulled it off.

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After Decades, NASA May Finally Replace Mars Relays

September 24, 2026 by Tom Nardi 21 Comments

We’ve yet to find any definitive evidence that there’s biological life on present-day Mars, but to say it’s a dead planet isn’t exactly accurate. Since the first Viking lander touched down in 1976, a revolving cast of humanity’s robotic envoys have worked on and around the Red Planet — and as access to space becomes cheaper and more routine, the mechatronic population of Mars will continue to grow.

Given the number of landers, rovers, and orbiting spacecraft that have been sent to study Mars over the last 50 years, you might be surprised to find that the communications systems in place to transmit all that critical scientific data back to Earth aren’t nearly as robust as you’d think. While it’s understandable that the first craft to arrive at Mars had to operate in isolation, even the flagship Perseverance and Curiosity rovers carry their own high-gain radio systems so they can communicate directly with Earth. Given the incredible premium put on the mass of an interplanetary craft, each mission that needs to bring along its own link back to Earth effectively reduces its payload of much scientific equipment.

It’s not that satellites in orbit around the planet aren’t used to relay signals between Martian ground assets and their controllers back on Earth. In fact these relay links are used extensively for bandwidth-intensive tasks such as image transfers. But it’s also true that the craft currently available to act as intermediaries between the two planets aren’t terribly well suited to the task. The current fleet of Mars orbiters were conceived primary as research vehicles, and so every decision regarding their design and positioning around the planet was made with that goal in mind. What relatively limited capability they do have as communication relays is further hindered by the age of their hardware.

But after decades of false starts and shifting budgets, NASA is closer than ever to finally establishing the Mars Telecommunications Network, a dedicated high-bandwidth communication relay that will ensure current and future missions always have a way to phone home.

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Searching For Dark Matter With A Levitating Magnet

September 21, 2026 by Maya Posch 31 Comments

Much of science is performed through inference, with the readings on instruments, a flash of light in heavy water, or the results of parsing through terabytes of sensor data after a particle accelerator collision either backing up a proposed scenario or weakening its foundations.

In the case of so-called dark matter, this is even more relevant, as we are talking about a proposed form of matter whose most pertinent feature is that it doesn’t interact with anything else except through gravity. This is where the wiggling of a levitating magnet may be the key to detecting it.

In this experimental setup by Rice University and Dutch researchers at the Leiden Institute, a tiny permanent magnet the size of a grain of sand is levitated above a superconductor, surrounded by highly sensitive detectors that should be able to spot even minuscule movements. So far, they have collected a month’s worth of data, with no conclusive results yet.

Even if they don’t detect any ‘knocks’ on this tiny levitating magnet, it will still help refine existing models of what dark matter’s properties might be. For the next phase of this research, they’ll add more of these sensors, which will also make it easier to distinguish background noise from any unusual readings.

We’ve previously talked about [Vera Ruben]’s contributions to the hunt for dark matter and the mysteries that prompted the idea that it might exist.