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On July 1st, 2023, the ESA’s Euclid mission headed for space, where it began its mission to observe the Universe and measure its expansion over time. The commissioning process began well as the mission team spent weeks testing and calibrating the observatory, then flew the mission out to Lagrange Point 2 (LP2). The telescope focused its mirrors, collected its “first light,” and the first test images it took were breathtaking! Unfortunately, Euclid hit a snag when its Fine Guidance Sensor (FGS) failed to lock onto its “guide stars.”

According to the latest update from the ESA, Euclid has found its guide stars again, thanks to a software patch. With its navigation woes now solved and its observation schedule updated, the telescope will now undergo its Performance Verification phase (its final phase of testing) in full “science mode.” Once that’s complete, Euclid will commence its nominal six-year mission, providing razor-sharp images and deep spectra of our Universe, looking back 10 billion years. This data will be used to create a grand survey of one-third of the entire sky and measure the influence of Dark Matter and Dark Energy.

The Euclid mission is one of the most sophisticated and precise observatories ever launched. To ensure accuracy, the telescope must point to a new field in the sky every 75 minutes with extreme stability. To do this, the spacecraft relies on the Fine Guidance Sensor (FGS), a completely new instrument that uses optical sensors to image the sky from the sides of Euclid’s VISible instrument (VIS). This allows the telescope to lock onto stars found by ESA’s Gaia mission, using them for navigation and determining where the telescope needs to be pointed.

Loopy star trails show the effect of Euclid s Fine Guidance Sensor intermittently losing its guide stars pillars 1024x1024 2
Loopy star trails show the effect of Euclid’s Fine Guidance Sensor intermittently losing its guide stars. Credit: ESA

This information is relayed to the telescope’s Attitude and Orbit Control System (AOCS), which controls Euclid’s orientation and orbital motion. However, cosmic rays and solar flares can cause false signals (artefacts) to appear in Euclid’s observations, which can also be caused by stray sunlight and X-rays. These false signals intermittently outnumbered real stars in the telescope’s field of view, which led to Euclid’s FGS failing to resolve the star patterns it needed to navigate. This led to a series of test images with swirling star trails and “lassos” as the telescope failed to home in on its target.

The software patch was tested first on Earth with an electric model of Euclid and a simulator, then for ten days in orbit. As Micha Schmidt, Euclid‘s Spacecraft Operations Manager, explained in an ESA press release:

“Our industrial partners – Thales Alenia Space and Leonardo – went back to the drawing board and revised the way the Fine Guidance Sensor identifies stars. After a major effort and in record time, we were provided with new on-board software to be installed on the spacecraft. We carefully tested the software update step by step under real flight conditions, with realistic input from the Science Operations Centre for observation targets, and finally the go-ahead was given to re-start the Performance Verification phase.”

The software patch was first tested using an

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Neutron Star is Spraying Jets Like a Garden Sprinkler

Cowie1 s shape jet

X-ray binaries are some of the oddest ducks in the cosmic zoo and they attract attention across thousands of light-years. Now, astronomers have captured new high-resolution radio images of the first one ever discovered. It’s called Circinus X-1. Their views show a weird kind of jet emanating from the neutron star member of the binary. The jet rotates like an off-axis sprinkler as it spews material out through surrounding space, sending shockwaves through the interstellar medium.

The MeerKAT radio telescope in South African spotted the S-shaped jets emanating from the neutron star. Its images are the first-ever high-resolution views of such jets, according to lead researcher Fraser Cowie. “This image is the first time we have seen strong evidence for a precessing jet from a confirmed neutron star,” he said, referring to the neutron star’s off-axis spin. “This evidence comes from both the symmetric S shape of the radio-emitting plasma in the jets and from the fast, wide shockwave, which can only be produced by a jet changing direction.”

Such an awkward spin gives the jets their peculiar S-like configuration. Since scientists aren’t completely sure what phenomena caused them to launch in the first place, studying the odd behavior gives insight into the extreme physics behind its existence.

Examining the Neutron Star Jets in Detail

The MeerKAT measurements showed not only the jet but revealed termination shocks moving away from the neutron star. These occur in regions where the jets slam into material in surrounding space. This is the first time astronomers found such shocks around an X-ray binary like Circinus X-1. Those waves are moving fast—at about 10 percent the speed of light and their structure points back to the jet as their source. “The fact that these shockwaves span a wide angle agrees with our model,” Cowie said. “So we have two strong pieces of evidence telling us the neutron star jet is processing.”

A MeerKAT radio image of the S-shape jet precessing in the Circinus X-1 X-ray binary pair system. The jet emanates as a result of the accretion of material around the neutron star. Courtesy: Fraser Cowie, Attribution CC BY 4.0.
A MeerKAT radio image of the S-shape jet precessing in the Circinus X-1 X-ray binary pair system. The jet emanates as a result of the accretion of material around the neutron star. Courtesy: Fraser Cowie, Attribution CC BY 4.0.

The speed of those shockwaves turns them into particle accelerators producing high-energy cosmic rays. The fact that those rays exist tells astronomers the action around the X-ray binary is extremely energetic. That high-energy activity has grabbed astronomers’ attention for half a century. Still, it remains a mysterious system, so as Cowie points out, it’s important to observe the jets and see how their behavior changes over time. “Several aspects of its behavior are not well explained so it’s very rewarding to help shed new light on this system, building on 50 years of work from others,” he said. “The next steps will be to continue to monitor the jets and see if they change over time in the way we expect. This will allow us to more precisely measure their properties and continue to learn more about this puzzling object.”

bout Circinus X-1

The Circinus X-1 system contains a neutron star and a companion. The pair lies some 30,000 light-years away in the direction of the southern hemisphere constellation Circinus. It was first spotted in June 1969 by an Aerobee suborbital rocket carrying X-ray-sensitive instruments and has been studied for years by astronomers using optical, X-ray, and radio telescopes.

Composite image of Circinus X-1, which is about 24,000 light-years from Earth in the constellation Circinus. Credit: X-ray: NASA/CXC/Univ. of Wisconsin-Madison/S. Heinz et al; Optical: DSS; Radio: Did you miss our previous article…
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Experimental Radar Technique Reveals the Composition of Titan’s Seas

Cassini Titan bistatic schematic 1024x523 1

The Cassini-Huygens mission to Saturn generated so much data that giving it a definitive value is impossible. It’s sufficient to say that the amount is vast and that multiple scientific instruments generated it. One of those instruments was a radar designed to see through Titan’s thick atmosphere and catch a scientific glimpse of the moon’s extraordinary surface.

Scientists are still making new discoveries with all this data.

Though Saturn has almost 150 known moons, Titan attracts almost all of the scientific attention. It’s Saturn’s largest moon and the Solar System’s second largest. But Titan’s surface is what makes it stand out. It’s the only object in the Solar System besides Earth with surface liquids.

Cassini’s radar instrument had two basic modes: active and passive. In active mode, it bounced radio waves off surfaces and measured what was reflected back. In passive mode, it measured waves emitted by Saturn and its moons. Both of these modes are called static modes.

But Cassini had a third mode called bistatic mode that saw more limited use. It was experimental and used its Radio Science Subsystem (RSS) to bounce signals off of Titan’s surface. Instead of travelling back to sensors on the spacecraft, the signals were reflected back to Earth, where they were received at one of NASA’s Deep Space Network (DNS) stations. Critically, after bouncing off of Titan’s surface, the signal was split into two, hence the name bistatic.

A team of researchers has used Cassini’s bistatic data to learn more about Titan’s hydrocarbon seas. Their work, “Surface properties of the seas of Titan as revealed by Cassini mission bistatic radar experiments,” has been published in Nature Communications. Valerio Poggiali, a research associate at the Cornell Center for Astrophysics and Planetary Science, is the lead author.

This schematic shows how Cassini's bistatic radar experiment worked. The orbiter used its Radio Science Subsystem to send signals to Titan's surface. The signals then reflected off of Titan to Earth, where they were received by either the DNS receiver at Canberra, Goldstone, or Madrid. The signals are either Right Circularly Polarized (RCP) or Left Circularly Polarized (LCP.) Image Credit: Poggiali et al. 2024.
This schematic shows how Cassini’s bistatic radar experiment worked. The orbiter used its Radio Science Subsystem to send signals to Titan’s surface. The signals then reflected off Titan to Earth, where they were received by one of the DNS receivers at Canberra, Goldstone, or Madrid. The signals are either Right Circularly Polarized (RCP) or Left Circularly Polarized (LCP). Image Credit: Poggiali et al. 2024.

The signals that reach the DNS are polarized, which reveals more information about the hydrocarbon seas on Titan. While Cassini’s radar instrument revealed how deep the seas are, the bistatic radar data tells researchers about both their compositions and surface textures.

This image of the hydrocarbon seas on Titan is well-known and was radar-imaged by Cassini. That radar data told us how deep the seas are. New bistatic radar data can reveal more about the composition and surface texture of the seas. Image Credit: [JPL-CALTECH/NASA, ASI, USGS]
This image of the hydrocarbon seas on Titan is well-known and was radar-imaged by Cassini. That radar data told us how deep the seas are. New bistatic radar data can reveal more about the composition and surface texture of the seas. Image Credit: [JPL-CALTECH/NASA, ASI, USGS]

“The main difference,” Poggiali said, “is that the bistatic information is
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Webb Measures the Weather on a Tidally Locked Exoplanet

Webb Atmosphere Graphic 1024x663 1

Exploring exoplanet atmospheres in more detail was one task that planetary scientists anticipated during the long wait while the James Webb Space Telescope (JWST) was in development. Now, their patience is finally paying off. News about discoveries of exoplanet atmosphere using data from JWST seems to be coming from one research group or another almost every week, and this week is no exception. A paper published in Nature by authors from a few dozen institutions describes the atmospheric differences between the “morning” and “evening” sides of a tidally locked planet for the first time.

First, let’s clarify what the “morning” and “evening” sides mean. Tidally locked planets don’t spin, so one hemisphere constantly faces the planet’s star. As such, there is always a part of the planet where it appears to be “morning,” with the star barely peaking over the horizon. Alternatively, there’s a part of the planet where it seems to be “evening,” where the star is again just barely peaking over the horizon, but it would appear to be setting. 

Typically, on Earth, we would think of the morning side as the star peaking over the eastern side, whereas the evening side would see the star setting into the western sky. However, exoplanets sometimes rotate in the opposite direction from planets in our solar system, so that mental model doesn’t always work for them.

Webb Atmosphere Graphic 1024x663 2
The JWST light curve for WASP-34b, clearly showing the dip in the star’s brightness as the planet passes in front of it.
Credit – NASA / ESA / CSA / R. Crawford (STScI)

It’s also important not to confuse the “morning” and “evening” sides with the “day” and “night” sides of the planet. On the day side, the full force of the star affects the planet, but on the night side, the star is never seen at all. The temperature differences on such a planet are massive, and cause much more extreme weather than anything we have experience with in our solar system.

That is the case for WASP-39b, one of the most studied exoplanets. It is a “hot Jupiter” and is roughly 1.3 times the size of the largest planet in our solar system, though it only masses in at about the same size as Saturn. It’s 700 light years away and is tidally locked to its star.

Exoplanet hunters have intently studied this exoplanet since its discovery in 2011. It was the target of JWST’s first exoplanet research when it began science operations. Since then, they’ve made several interesting discoveries, and the Nature paper describes a new one—that the “morning” side of WASP-39b is a few hundred degrees cooler than its “evening” side.

Fraser talks exoplanet atmosphere with expert Dr. Joanna Barstow.

This temperature discrepancy is likely due to atmospheric conditions on the planet itself. The paper’s authors believe there is an extremely strong wind on the planet that runs from day to night at thousands of miles an hour. The wind rotates from the day side through the evening side to the night side, then through the morning side back to the day side.

So, essentially, the morning side receives “air” that has been cooled while traveling through the planet’s night side. However, that air is still a blistering 600 C (1,150 F). The temperature on the evening side, though, is hotter at 800 C (1,450 F), much hotter than any conditions found on any planet in our solar system.

Detecting such a temperature difference on an exoplanet hundred of light years away is an impressive technical feat, and the study’s lead author, Néstor Espinoza, credits JWST’s capabilities for enabling it. The telescope watched the planet both while it was traversing in front of its star, but also while it was next to it and emitting its own, admittedly much fainter, light. 

JWST found methane in a different exoplanet atmosphere, as Fraser describes in this video.

They were differentiating between the starlight filtered through the atmosphere of the planet and when there was no filtered starlight coming through allowed the researchers to make temperature estimates. JWST is so sensitive they were also able to split the data into semi-circles to differentiate the”
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