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NASA’s James Webb Space Telescope (JWST) has only been operational for just over a year, but this isn’t stopping the world’s biggest space agency from discussing the next big space telescope that could serve as JWST’s successor sometime in the future. Enter the Habitable Worlds Observatory (HWO), which was first proposed as NASA’s next flagship Astrophysics mission during the National Academy of Sciences’ Decadal Survey on Astronomy and Astrophysics 2020 (Astro2020). While its potential technological capabilities include studying exoplanets, stars, galaxies, and a myriad of other celestial objects for life beyond Earth, there’s a long way to go before HWO will be wowing both scientists and the public with breathtaking images and new datasets.

“Before we can design the mission, we need to develop the key technologies as much as possible,” said Dr. Dimitri Mawet, who is a Professor of Astronomy at Caltech and a Senior Research Scientist at the NASA Jet Propulsion Laboratory (JPL). “We are in a phase of technology maturation. The idea is to further advance the technologies that will enable the Habitable Worlds Observatory to deliver its revolutionary science while minimizing the risks of cost overruns down the line.”

Dr. Mawet is one of 56 individuals who have been selected to be part of the Technical Assessment Group (TAG) for HWO, which is scheduled to hold their first meetings in Washington D.C. between October 31 and November 2, 2023. As part of these meetings, the individuals will be comprised of two groups as part of NASA’s “Great Observatory Maturation Program” (GOMAP): Science, Technology, Architecture Review Team (START) and a Technical Assessment Group (TAG), with a full member list for both teams available here. While START will focus on HWO’S science goals, TAG will focus on HWO’S design and the necessary technology to meet the design requirements.

“The Decadal Survey recommended this mission as its top priority because of the transformational capabilities it would have for astrophysics, together with its ability to understand entire solar systems outside of our own,” said Dr. Fiona Harrison, who co-chaired the Astro2020 decadal report committee and is a Harold A. Rosen Professor of Physics and the Kent and Joyce Kresa Leadership Chair of the Division of Physics, Mathematics and Astronomy, both at Caltech.

For now, trying to identify biosignatures on exoplanets is limited to studying their atmospheres using spectroscopy, a method that involves analyzing light to identify any gases that might be present. A key aspect of analyzing exoplanet atmospheres is blocking out the immense glare from an exoplanet’s parent star, leaving only faint starlight that reflects off a nearby exoplanet’s atmosphere. This blocking of star glare is conducted with one of two primary ways: a coronagraph and a starshade.

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Credit: European Space Agency

First invented by French astronomer Dr. Bernard Lyot in 1939 to study our Sun, a coronagraph is internal to the telescope and blocks out starlight through a multi-step process involving a mask, a washer (also called a Lyot stop), and a special mirror all working in tandem to first reduce large amounts of starlight coming into the telescope and finally revealing the exoplanets that were hiding within the star’s glare. Astronomers then can use spectroscopy to analyze the light from these exoplanets to identify gases within their respective atmospheres.

Currently, NASA’s Hubble Space Telescope and JWST are the only space telescopes that use coronagraphs to study exoplanets, along with several ground-based telescopes, including the European Southern Observatory’s (ESO) Very Large Telescope (VLT), the Gemini Planet Imager, and telescopes located at the Keck Observatory in Hawaii. Going forward, there are plans for NASA’s upcoming Nancy Grace Roman Space Telescope (often shortened as the Roman Space Telescope) to use an advanced coronagraph known as the Coronagraphic Instrument (CGI) for imaging gaseous exoplanets, with Roman slated to launch onboard a SpaceX Falcon Heavy sometime in 2027.

If a coronagraph is internal to the telescope, the starshade is its external counterpart. While no current space telescopes employ starshades, development models designed and built by NASA would detach from a future
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The Solar Wind is Stripping Oxygen and Carbon Away From Venus

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The BepiColombo mission, a joint effort between JAXA and the ESA, was only the second (and most advanced) mission to visit Mercury, the least explored planet in the Solar System. With two probes and an advanced suite of scientific instruments, the mission addressed several unresolved questions about Mercury, including the origin of its magnetic field, the depressions with bright material around them (“hollows”), and water ice around its poles. As it turns out, BepiColombo revealed some interesting things about Venus during its brief flyby.

Specifically, the two probes studied a previously unexplored region of Venus’ magnetic environment when they made their second pass on August 10th, 2021. In a recent study, an international team of scientists analyzed the data and found traces of carbon and oxygen being stripped from the upper layers of Venus’ atmosphere and accelerated to speeds where they can escape the planet’s gravitational pull. This data could provide new clues about atmospheric loss and how interactions between solar wind and planetary atmospheres influence planetary evolution.

The study was led by Lina Hadid, a CNRS researcher at the Plasma Physics Laboratory (LPP) and the Observatoire de Paris. She was joined by researchers from the Institute of Space and Astronautical Science (ISAS) at JAXA, the Max Planck Institute for Solar System Research (MPS), the CNRS Research Institute in Astrophysics and Planetology (IRAP), the Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), the Institute for Geophysics and Extraterrestrial Physics (IGEP), the Space Research Institute (SRI), and multiple universities.

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Schematic view of planetary material escaping through Venus magnetosheath flank. Credit: Thibaut Roger/Europlanet 2024 RI/Hadid et al.

While Venus does not have an intrinsic magnetic field like Earth, it has a weak magnetic field that results from the interaction of solar wind and electrically charged particles in Venus’ upper atmosphere. Surrounding this “induced magnetosphere” is the “magnetosheath,” a region where the solar wind is slowed and heated. In August 2021, BepliColombo’s two spacecraft – the ESA’s Mercury Planetary Orbiter (MPO) and JAXA’s Mercury Magnetospheric Orbiter (MMO, aka. Mio) – passed by Venus on the final leg of their journey toward Mercury, using the planet’s gravity to adjust its course and its upper atmosphere to shed speed.

The two spacecraft spent 90 minutes passing through the tail of the magnetosheath and the magnetic regions closest to the Sun. The mission controllers used this opportunity to gather data on the number and mass of charged particles it encountered using Mio‘s Mass Spectrum Analyzer (MSA) and the Mercury Ion Analyzer (MIA), which are part of the probe’s Mercury Plasma Particle Experiment (MPPE). The team also relied on Europlanet’s Sun Planet Interactions Digital Environment on Request (SPIDER) space weather modeling tools to track how atmospheric particles propagated through the magnetosheath.

As Hadid explained in a Europlanet Society release, analysis of this data provides insight into the chemical and physical processes driving atmospheric escape from this region of the magnetosheath:

“This is the first time that positively charged carbon ions have been observed escaping from Venus’s atmosphere. These are heavy ions that are usually slow moving, so we are still trying to understand the mechanisms that are at play. It may be that an electrostatic ‘wind’ is lifting them away from the planet, or they could be accelerated through centrifugal processes.”

In particular, these findings could help scientists to deduce what happened to Venus’ surface water. Like Earth, much of Venus’ surface was once covered in oceans, which disappeared about 700 million years ago. The most widely-held theory is that this coincided with a massive resurfacing event that flooded the atmosphere with carbon
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Are Titan’s Dunes Made of Comet Dust?

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A new theory suggests that Titan’s majestic dune fields may be have come from outer space. Researchers had always assumed that the sand making up Titan’s dunes was locally made, through erosion or condensed from atmospheric hydrocarbons. But researchers from the University of Colorado want to know: Could it have come from comets?

The dunes of Titan

When the Cassini spacecraft arrived in orbit around Saturn, nobody had ever seen beneath the thick soupy atmosphere of Titan. So when it dropped the Huygens lander, and began probing Titan with cloud-penetrating radar, scientists were surprised to learn that Titan has a very earth-like appearance. It has a thick nitrogen atmosphere, rain, rivers, oceans and massive dune fields. But unlike the dunes of Earth’s sandy deserts in Namibia and southern Arabia, Titan’s dunes are enormous, and fill massive fields covering more than an eighth of the giant moon’s surface. These dunes are about 100 meters tall, 1 to 2 km wide at the base, and can stretch for hundreds of kilometers in length.

Dunes on Earth are made from sand, which is blown by the wind and heaped into drifts. Individual sand particles are nudge and blown by the wind with enough force to make them bounce and scatter, in a process called saltation. If the particles don’t bounce, then they cannot pile up on top of each other, but if the wind is able to lift them off the ground completely then they simply blow away. Saltation depends on the size and mass of the sand particles and the strength of the wind, but also needs the particles to be dry so that they can move freely without sticking together.

Titan’s geology

Titan is the second largest moon in the entire Solar System, beaten only by Ganymede, orbiting Jupiter. It is Saturn’s largest moon, and very old. Unlike most of Saturn’s moon, which were captured over time, Titan would have formed together with Saturn billions of years ago. Despite having so many features in common with Earth, it is a very different place. It is so intensely cold that, instead of water, its rain and rivers are made from liquid hydrocarbons like methane. Water, on the other hand, is frozen into hard ice; rocks on Titan are made from water ice, instead of granite and basalt, and Titan’s equivalent of lava and magma are made from liquid water and ammonia.

This means that sand on Titan is not made from silica eroded from larger rocks, since those materials are not found on the surface. One popular theory is that it could instead be made from ice. When liquid methane rains and flows, it could erode the water-ice bedrock, grinding chunks together to a sand of ice grains. An alternative idea is that the sand particles are instead made from tholins. These are found all over the colder regions of the Solar System, where cold hydrocarbons in comets or the outer atmospheres of planets and moons react with ultraviolet light from the Sun to create complex compounds. Tholins formed in the dry atmosphere of Titan could clump together with static electricity to form small grains of soot that then settle to the ground, creating both dust and sand.

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Comet 109P/Swift-Tuttle captured during its last pass by Earth on Nov. 1, 1992. Credit: Gerald Rhemann

What do comets have to do with this?

But a paper presented at this year’s Lunar and Planetary Science Conference (LPSC) suggests a new idea: What if the sand came from comets? Comets, as we know, are made from materials left over from the creation of the Solar System. Most of the primordial gas and dust that collapsed from an ancient nebula to form the Solar System would have ended up in the Sun, with the bulk of the remains forming the planets. But this still would still have left a lot of material floating free, and some of that would have gradually coalesced into lumps of dust and ices, which we see today as comets. When comets are nudged into elliptical orbits and pass through the inner Solar System, some of their ice heats up and sublimates into gas which blows out, carrying dust with it. This dust is scattered throughout the Solar System, concentrated along the various comet’s orbits. Individual grains often collide with the Earth, which we see as meteors, burning high in our atmosphere. Recent surveys in Antarctic ice

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The Milky Way’s Most Massive Stellar Black Hole is Only 2,000 Light Years Away

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Astronomers have found the largest stellar mass black hole in the Milky Way so far. At 33 solar masses, it dwarfs the previous record-holder, Cygnus X-1, which has only 21 solar masses. Most stellar mass black holes have about 10 solar masses, making the new one—Gaia BH3—a true giant.

Supermassive black holes (SMBH) like Sagittarius A Star at the heart of the Milky Way capture most of our black hole attention. Those behemoths can have billions of solar masses and have enormous influence on their host galaxies.

But stellar-mass holes are different. Unlike SMBHs that grow massive through mergers with other black holes, stellar black holes result from massive stars exploding as supernovae. SMBHs are always found in the center of a massive galaxy, but stellar black holes can be hidden anywhere.

“This is the kind of discovery you make once in your research life.”

Pasquale Panuzzo, National Centre for Scientific Research (CNRS) at the Observatoire de Paris

Astronomers found BH3 in data from the ESA’s Gaia spacecraft. It’s Gaia’s third stellar black hole. BH3 has a stellar companion, and the black hole’s 33 combined solar masses tugged on its aged, metal-poor companion. The star’s tell-tale wobbling betrayed BH3’s presence. At only 2,000 light-years away, BH3 is awfully close in cosmic terms.

Astronomers have found the most massive stellar black hole in our galaxy, thanks to the wobbling motion it induces on a companion star. This artist's impression shows the star's orbits and the black hole, dubbed Gaia BH3, around their common centre of mass. The European Space Agency's Gaia mission measured this wobbling over several years. Image Credit: ESO/L. Calçada
Astronomers have found the most massive stellar black hole in our galaxy, thanks to the wobbling motion it induces on a companion star. This artist’s impression shows the star’s orbits and the black hole, dubbed Gaia BH3, around their common centre of mass. The European Space Agency’s Gaia mission measured this wobbling over several years. Image Credit: ESO/L. Calçada

A new research letter in Astronomy and Astrophysics presented the discovery. Its title is “Discovery of a dormant 33 solar-mass black hole in pre-release Gaia astrometry.” The lead author is Pasquale Panuzzo, an astronomer from the National Centre for Scientific Research (CNRS) at the Observatoire de Paris.

“No one was expecting to find a high-mass black hole lurking nearby, undetected so far,” said Panuzzo. “This is the kind of discovery you make once in your research life.”

This black hole is remarkable for its considerable mass. Researchers have found stellar black holes with similar masses, but always in other galaxies. The size is confounding, but astrophysicists have pieced together how they may become so massive.

They could result from the collapse of metal-poor stars. These stars are composed almost entirely of hydrogen and helium, the primordial elements. Scientists think these stars lose less mass over their lifetimes of fusion than other stars. They retain more mass, so they collapse into more massive black holes. This idea is based on theory; there’s no direct evidence.

But BH3 could change that.

Binary stars tend to form together and have the same metallicity. Follow-up observations showed that BH3’s companion star is likely a remnant of a globular cluster that the Milky Way absorbed more than eight billion years ago. Since binary stars tend to have the same metallicity, this metal-poor companion bolsters the idea that low-metallicity stars can retain more mass and form larger stellar black holes. This is the first evidence supporting the idea that ancient and metal-poor massive stars collapse into massive black holes. It also supports the idea that these early stars may have evolved differently than modern stars of similar masses.

But there’s another interpretation.

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