Establishing a New Habitability Metric for Future Astrobiology Surveys

The search for exoplanets has grown immensely in recent decades thanks to next-generation observatories and instruments. The current census is 5,766 confirmed exoplanets in 4,310 systems, with thousands more awaiting confirmation. With so many planets available for study, exoplanet studies and astrobiology are transitioning from the discovery process to characterization. Essentially, this means that astronomers are reaching the point where they can directly image exoplanets and determine the chemical composition of their atmospheres.

As always, the ultimate goal is to find terrestrial (rocky) exoplanets that are “habitable,” meaning they could support life. However, our notions of habitability have been primarily focused on comparisons to modern-day Earth (i.e., “Earth-like“), which has come to be challenged in recent years. In a recent study, a team of astrobiologists considered how Earth has changed over time, giving rise to different biosignatures. Their findings could inform future exoplanet searches using next-generation telescopes like the Habitable Worlds Observatory (HWO), destined for space by the 2040s.

The study was led by Kenneth Goodis Gordon, a graduate student with the University of Central Florida’s (UCF) Planetary Sciences Group. He was joined by researchers from the SETI Institute, the Virtual Planetary Laboratory Team at the University of Washington, NASA’s Nexus for Exoplanet System Science (NESS), the Space Science Division and Astrobiology Division at the NASA Ames Research Center, the Sellers Exoplanet Environments Collaboration (SEEC) at the NASA Goddard Space Flight Center, and NASA’s Jet Propulsion Laboratory. The paper that describes their findings is being considered for publication in The Astrophysical Journal.

Artist concept of Earth during the Late Heavy Bombardment period. Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab.

As the team indicates in their paper, the current census of exoplanets includes more than 200 terrestrial planets, dozens of which have been observed in their parent stars’ habitable zone (HZ). Many more are expected in the coming years, thanks to next-generation instruments like the James Webb Space Telescope (JWST) and the ESO’s Extremely Large Telescope (ELT). Equipped with cutting-edge spectrometers, adaptive optics, and coronographs, these and other telescopes will enable the characterization of exoplanets, identify biosignatures, and determine their habitability.

This is a complex problem since a range of different planetary, orbital, and stellar parameters must be considered. To date, Earth is the only planet known to harbor life, which limits our perspective. But as Goodis Gordon told Universe Today via email, this is not the only way in which habitability studies have been constrained:

“Currently, there is only one example of a planet known to harbor life: our own Earth. However, when we think of habitability, most of the time, people will only relate that term to modern-day Earth-like conditions: large-scale vegetation, animals, humans, etc. This can severely limit our approach to finding habitable exoplanets because it only provides us with one data point to compare against.

“But we know from biogeochemical analyses that the Earth is not just one data point and that our planet has actually been habitable for eons. So better understanding the signatures of the Earth throughout its evolution provides us with more comparison points when searching for habitable worlds elsewhere.”

For instance, life emerged on Earth during the Archeon Eon (ca. 4 billion years ago), when the atmosphere was predominantly composed of nitrogen, carbon dioxide, methane, and inert gases. By the late Paleoproterozoic Era (ca. 2.5 to 1.6 billion years ago), the Great Oxygenation Event occurred after a billion years of cyanobacterial photosynthesis. This period lasted from 2.46 to 2.06 billion years ago and caused Earth’s atmosphere to transition from a reducing atmosphere to an oxidizing atmosphere, which led to the emergence of more complex life forms.

Artist’s impression of Earth during the Archean Eon. Credit: Smithsonian National Museum of Natural History

During this same period, the Sun underwent evolutionary changes over the past 4.5 billion years. At this time, the Sun was 30% dimmer than it is today and has gradually grown brighter and hotter since. Despite this, Earth maintained liquid water on its surface, and life continued to survive and evolve. The complex interrelationship between Earth’s evolving atmosphere and our Sun’s evolution is key to maintaining habitability for billions of years. As Goodis Gordon explained:

“In addition to that, current exoplanet characterization strategies tend to rely solely on the unpolarized light received from these worlds, which studies have shown can result in errors in the retrieved fluxes and degeneracies in the calculated planetary parameters. For example, if an exoplanet has really thick clouds or hazes in its atmosphere, the observed flux spectrum can be flat with almost no spectral features. This makes it extremely difficult to detect what gases are in the atmosphere or even what those clouds or hazes that blocked the light are made of.”

In recent years, several studies have examined the flux and polarization signatures of light reflected by an early Earth. Others have simulated different scenarios throughout the Archean, Proterozoic (2.5 billion to 541 million years ago), and Phanerozoic Eons (538.8 million years ago to the present). Lastly, some studies analyzed how the signatures of these early-Earth analogs would change if they orbited different types of stars. But as Goodis Gordon pointed out, nearly all of these studies focused on the unpolarized flux from these worlds, so they missed some of the information available in the light:

“Polarization is a more sensitive tool than flux-only observations and can enhance exoplanet characterizations. Polarimetry is extremely sensitive to the physical mechanism scattering the light, thereby allowing for accurate characterizations of the properties of a planetary atmosphere and surface. Also, since polarization measures light as a vector, it is sensitive to the locations of features on the planet, such as cloud and land distributions, as well as diurnal rotation and seasonal variability. Within the Solar System, polarimetric observations helped characterize the clouds of Titan, Venus, and the gas giants, while outside of it, polarimetry has been used to characterize the cloud properties of brown dwarfs. In most of these cases, the characterizing discovery was possible only with polarimetry!”

This artist’s concept features one of multiple initial possible design options for NASA’s Habitable Worlds Observatory. Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab

This could have profound implications for the study and characterization of exoplanets in the near future. Using an expanded concept of habitability that takes into account how Earth has evolved over time and benefits from the study of polarized light, astronomers will likely identify far more habitable planets when next-generation observatories like the HWO become available. The plans for this observatory build upon two earlier mission concepts – the Large Ultraviolet Optical Infrared Surveyor (LUVOIR) and the Habitable Exoplanets Observatory (HabEx).

Based on these previous studies and the experience astronomers have accrued by working with previous exoplanet-hunting missions—i.e., Hubble, Kepler, the Transiting Exoplanet Survey Satellite (TESS), and the JWST—the HWO will be designed specifically to examine the “atmospheres of exoplanets for potential indications of life” (aka “biosignatures”) and determine if they are potentially habitable planets. As Goodis Gordon indicated, his team’s research could help inform future surveys using the HWO and other next-generation observatories:

“Our models provide more data points to compare observations of terrestrial exoplanets against and therefore help to inform habitability studies of these worlds. Additionally, there has been a push in the exoplanet community in recent years to include polarimetry in near-future observatories like the Extremely Large Telescopes on the ground or the Habitable Worlds Observatory in space. Our hope is that our models will help prove the power of polarimetry in characterizing and distinguishing between different habitable exoplanet scenarios in ways that unpolarized flux observations cannot.”

Further Reading: arXiv

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Astronomers Solve the Mystery of the Famed Brown Dwarf That is Too Bright: It’s Twins!

In 1995, Caltech researchers at the Institute’s Palomar Observatory first observed what appeared to be a brown dwarf orbiting Gliese 229 – a red dwarf star located about 19 light-years from Earth. Since then, this brown dwarf (Gliese 229 B) has mystified astronomers because it appeared too dim for its mass. With 70 times the mass of Jupiter, it should have been brighter than what telescopes had observed. However, a Caltech-led international team of astronomers recently solved the mystery by determining that the brown dwarf is a pair of closely orbiting twins!

The study was led by Jerry W. Xuan, a graduate student in Caltech’s Department of Astronomy working with Dimitri Mawet, the David Morrisroe Professor of Astronomy. They were joined by an international team from institutes and universities around the world, including the National Research Council of Canada Herzberg, the European Southern Observatory (ESO), the European Space Agency (ESA), the Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), the Max Planck Institute for Astronomy (MPIA) and Extraterrestrial Physics (MPE), and NASA’s Jet Propulsion Laboratory (JPL).

Their study, which appeared in Nature, was funded by NASA and the Heising-Simons Foundation. The study team responsible for discovering Gliese 229 B in 1995 included several co-authors on this latest study, including Rebecca Oppenheimer, a Caltech graduate student at the time (now an astrophysicist at the American Museum of Natural History); Shri Kulkarni, the George Ellery Hale Professor of Astronomy and Planetary Science; Keith Matthews, an instrument specialist at Caltech; and other colleagues.

At the time, their findings indicated that Gliese 229 B had methane in its atmosphere, which is typical of gas giants but not stars. These findings constituted the first confirmed detection of a brown dwarf, a class of cool star-like objects that constitute the “missing link” between gas giants and stars that had been predicted about 30 years prior. “Seeing the first object smaller than a star orbiting another sun was exhilarating,” said Oppenheimer in a Caltech news release, “It started a cottage industry of people seeking oddballs like it back then, but it remained an enigma for decades.”

“Gliese 229 B was considered the poster-child brown dwarf,” added Xuan. “And now we know we were wrong all along about the nature of the object. It’s not one but two. We just weren’t able to probe separations this close until now.” Hundreds of observations have been conducted since Gliese 229 B was discovered nearly 30 years ago, but its dimness remained a mystery to astronomers. While scientists suspected Gliese 229 B might be twins, the two brown dwarfs would have to be very close to each other to evade notice for almost three decades.

To confirm this theory, the team relied on the GRAVITY interferometer on the ESO’s Very Large Telescope in Chile to spatially resolve the two brown dwarfs. They then used the CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES+) instrument to detect their distinct spectral signatures and measure their Doppler shift. Their results showed that Gliese 229 B consists of two brown dwarfs (Gliese 229 Ba and Gliese 229 Bb) about 38 and 34 times the mass of Jupiter, that orbit each other with a period of 12 days and a separation of 16 times the distance between Earth and the Moon.

The observed brightness levels also match what is expected for two small brown dwarfs in this mass range. “This discovery that Gliese 229 B is binary not only resolves the recent tension observed between its mass and luminosity but also significantly deepens our understanding of brown dwarfs, which straddle the line between stars and giant planets,” said Mawet, a senior research scientist at NASA JPL. The discovery of this duo raises new questions about how tight-knit brown dwarfs form and suggests similar binaries may be out there and waiting to be found.

An artist’s conception of looking back at Sol from the binary brown dwarf system WISE 1049-5319, 6.5 light years distant. Credit: Janella Williams, Penn State University

Some theories suggest that brown dwarf pairs could form within a star’s protoplanetary disk that fragments into two seeds of brown dwarfs that become gravitationally bound after a close encounter. The same mechanism might lead to closely orbiting exoplanet binaries, though all of this remains to be seen. In the meantime, said Oppenheimer, this discovery is a very exciting development. “These two worlds whipping around each other are actually smaller in radius than Jupiter,” she said. “They’d look quite strange in our night sky if we had something like them in our own solar system. This is the most exciting and fascinating discovery in substellar astrophysics in decades.”

In the future, Xuan and his colleagues plan to search for more brown dwarf binaries using existing and next-generation instruments. This includes the Keck Planet Imager and Characterizer (KPIC) and the Keck Observatory’s High-resolution Infrared SPectrograph for Exoplanet Characterization (HISPEC). A team led by Mawet developed the former, while the latter is currently under construction at Caltech and other laboratories by teams also led by Mawet.

A separate independent study that appeared in The Astrophysical Journal Letters was led by Sam Whitebook and Tim Brandt, a Caltech graduate student and an associate astronomer at the Space Telescope Science Institute in Baltimore (respectively). Their findings also concluded that Gliese 229 B is a pair of tightly-orbiting brown dwarfs.

Further Reading: Caltech, Nature

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Hera Says Farewell to the Earth and Moon

Testing the equipment on an interstellar mission is one of the first things operators do when the spacecraft successfully launches. In some cases, those tests show the future troubles the mission will face, such as what happened to NASA’s Lucy mission a few years ago. However, in some cases, the mission provides us with perspectives we might never have seen before, which was the case for Hera, ESA’s mission to Dimorphos. This asteroid was deflected successfully during NASA’s DART test in 2022.

Hera was successfully launched on October 7th and carries a series of instruments designed to peer at the asteroids using different wavelengths. Some instruments were turned toward the Earth and Moon from about a million km away as part of the mission’s Near-Earth Commissioning Phase. The resulting pictures showcase the spacecraft’s capabilities and provide a new perspective of our “terraqueous globe,” as Carl Sagan once put it, and our much more sterile neighbor.

First, we have an image from the Asteroid Framing Camera or AFC. Technically comprised of two cameras (for redundancy, as so many space missions do), this monochrome 1020×1020 image is the clearest of the three released by ESA as part of a press release. It gives a sense of the scale of the distance between the Earth and the Moon, which can be hard to judge when down on the planet’s surface.

Image of the Earth (left) and Moon from Hera’s AFC.
Credit – ESA

Next up is the Thermal Infrared Imager, or TIRI. This one was taken slightly closer, at 1.4 million kilometers away (about three times the distance from the Earth to the Moon itself). TIRI is designed to capture infrared wavelengths of light – which we usually think of as heat. Watching Dimorphos over time will allow it to understand the “thermal inertia” of certain regions, which scientists can use to discern some important physical properties of the asteroid. While not the most exciting space image ever captured, the successful operation of this sensitive instrument is critical to the mission.

Image of the Earth (center) and Moon from Hera’s TIRI.
Credit – ESA

Finally, there’s Hyperscout H. It, too, is designed to capture Dimorphos in wavelengths that humans can’t visibly see – in this case, 650 nm to 950 nm wavelengths, which is considered “near infrared” as compared to the “mid-infrared” capabilities of TIRI. Also, this imager comes with its own false color depiction, showing “shorter” wavelengths, which are closer to our visible spectrum, as shades of blue, whereas “reds” represent wavelengths farther away from visible light. 

Image of Earth (bottom left) and Moon from Hera’s Hyperscout H imager.
Credit – ESA

The Earth and Moon have been imaged most likely millions of times in these wavelengths before, so it’s unlikely that any science will be gleaned from these images. Still, these images are invaluable as proof of concept for the operation of the systems. The three cameras comprise some of the essential parts of Hera’s “asteroid deck,” which houses most of the spacecraft’s other instruments, including two CubeSat deployers, a laser rangefinder, and antennas for deep-space communication with Earth. Many of those different instruments will have to wait until “show time” when the craft arrives at the binary asteroid system in December 2026. Hopefully, we will also receive plenty more images from the three systems covered here.

Learn More:
ESA – Hera’s first images offer parting glimpse of Earth and Moon
UT – Hera Probe Heads Off to See Aftermath of DART’s Asteroid Impact
UT – ESA’s Hera Mission is Bringing Two Cubesats Along. They’ll Be Landing on Dimorphos
UT – The Smallest Radar Ever Sent to Space Will Probe the Interior of Dimorphos After its Impact From DART

Lead Image:
Image of Earth from the AFC
Credit – ESA

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Giant Cluster is Spitting Out Massive Stars

We live inside the Milky Way galaxy which is joined as it drifts through space by two satellite galaxies, the Magellanic Clouds. A star cluster in the Large Magellanic Cloud known as R136 has been the subject of a fascinating discovery. A team of astronomers have discovered 55 high-speed stars that have been ejected from the cluster. The discovery was made using the Gaia satellite and it seems up to a third of stars from the cluster have been ejected in the last century. 

R136 is a massive star cluster in the Tarantula Nebula inside the Large Magellanic Cloud (LMC.) The LMC is a satellite galaxy of ours at a distance of around 160,000 light years. The cluster is among the most massive known and it contains some of the most massive stars ever observed. The stars are young at just a few million years old having formed out of the gas in the nebula. 

This is a Hubble Space Telescope image of a star-forming region containing massive, young, blue stars in 30 Doradus, the Tarantula Nebula. Located within the Large Magellanic Cloud, this is one of the regions observed by a newly-completed survey named ULLYSES. Image Credit: NASA, ESA, STScI, Francesco Paresce (INAF-IASF Bologna), Robert O’Connell (UVA), SOC-WFC3, ESO

When clusters form, the random movement of gas is transferred to the forming stars. With the movement of stars, crisscrossing the cluster it is not uncommon for stars to be ejected out. This was exactly what the team of astronomers observed using Gaia. The Gaia space observatory was launched back in 2013 by the European Space Agency and has been precisely mapping stellar positions since.

Artist’s impression of the ESA’s Gaia Observatory. Credit: ESA

The team of astronomers led by University of Amsterdam PhD student Mitchel Stoop discovered the ejected stars travelling at speeds above 100,000 km/hr. You may have heard the saying ‘live fast, die young!’ Whether it’s true for humans is an interesting debate but it certainly seems true for stars. The most massive stars in the Universe fuse elements deep in their core at an alarming rate so will reach the end of their lives in just a few million years. Stars like those in R136 are a great example of this and, after being ejected to distances of around 1,000 light years, explode as supernova producing a neutron star or a black hole. 

The measurements showed too that the stars have not been ejected over one particular period of the cluster’s history. The first event seems to have taken place 1.8 million years ago just when the cluster formed. Another event seems to have occurred around 200,000 years ago. Comparing the two events revealed an interesting difference. In the first event during the formation of the cluster, the stars shot off in almost random directions but in the second event, the stars moved in one general direction. 

The co-author of the paper which was published in Nature, Alex de Koter said “We think that the second episode of shooting away stars was due to the interaction of R136 with another nearby cluster (that was only discovered in 2012). The second episode may foretell that the two clusters will mix and merge in the near future.” 

The discovery that a third of the stars have been ejected from their point of origin shows that, through the ejection, they can influence other regions of the galaxy. It is even possible that ejected stars through the history of the evolution of the Universe could have contributed to the reionization of the universe by ultraviolet light. In this era, the universe transitioned from being filled with ionised gas to a more neutral era  with electrons and protons combining to form neutral hydrogen atoms. 

Source : Dozens of massive stars launched from young star cluster R136

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China Releases its First Roadmap for Space Science and Exploration Through 2050.

China’s space program has advanced considerably since the turn of the century. In addition to developing heavy-launch vehicles like the Long March 5 and building a modular space station in orbit, China has also embarked on an ambitious program of lunar exploration (Chang’e) – which has launched six robotic missions to explore the Moon’s surface since 2007. These missions are paving the way for crewed missions to the Moon by 2030 and creating a permanent habitat around the Moon’s southern polar region – the International Lunar Research Station (ILRS).

They also plan to send crewed missions to Mars by 2033, which will culminate in the creation of a permanent base there too. Earlier today, the Chinese Academy of Sciences (CAS), the China National Space Administration (CNSA), and the China Manned Space Agency (CMSE) jointly released the country’s first long-term scheme for space science and exploration. Titled “National Medium—and Long-Term Development Plan for Space Science (2024-2050),” this plan elaborated on the basic principles, development goals, and roadmap for the country’s space science and exploration through 2050.

Tiangong Chinese space station. Credit: China Manned Space Agency.

The plan revealed five major scientific themes it hopes to accomplish in three developmental stages between now and mid-century. These five themes contain 17 priority areas for future breakthroughs, outlined by CAS Vice President Ding Chibiao at a press conference earlier today. According to statements released by The State Council of the People’s Republic of China and shared via the China Global Television Network (CGTN), they include:

• Extreme Universe: Exploring the origin and evolution of the Universe and revealing the physical laws under extreme cosmic conditions. Key areas under this theme include dark matter and extreme Universes, the origin and evolution of the Universe, and the detection of baryonic matter.
• Space-time Ripples: Detecting low-frequency and primordial gravitational waves and uncovering the nature of gravity and space-time. The priority is space-based gravitational wave detection.
• Panorama of the Earth and Sun: The exploration of the Sun, the Earth, and the heliosphere to unravel the physical processes and laws governing the complex interactions within the Sun-Earth system. Priority areas include Earth’s cycle systems, comprehensive observations of the Earth-Moon system, space weather observations, three-dimensional solar exploration, and heliosphere exploration.
• Habitable Planets: Exploring the habitability of celestial bodies in the Solar System and exoplanets. Key priorities include sustainable development, the origin and evolution of the Solar System, characterization of planetary atmospheres, the search for extraterrestrial life, and exoplanet detection.
• Biological and Physical Space Science: Revealing the laws of matter movement and life activities under space conditions to deepen our understanding of fundamental physics. Key areas include microgravity science, quantum mechanics, general relativity, and space life sciences.

The plan also outlined a three-stage development roadmap between 2024 and 2050. For the first stage (2024-2027), China will focus on maintaining the operation of the Tiangong space station, carrying out crewed missions to the Moon, and commencing the fourth phase of its Chang’e program – which includes the launch of the Chang’e-7 and -8 missions in 2026 and 2028, respectively – as well as its planned missions to Mars. According to the program, five to eight space science satellite missions will also be approved during the period.

Visualization of the ILRS from the CNSA Guide to Partnership (June 2021). Credit: CNSA

The second stage (2028 to 2035) will consist of the continued operation of the Tiangong space station (and expanding it to twice its current size), crewed missions to the Moon, and the construction of the ILRS. China is also expected to deploy about 15 space satellite missions during this phase. The third and final stage (2036 to 2050) calls for more than 30 space science missions to be implemented, with the intention of achieving “significant advancements in key areas reaching a world-leading level.”

Through this program, China hopes to address some of the most challenging fundamental questions and scientific issues of our time. This includes the nature of Dark Matter and Dark Energy, the origins of the Universe, extraterrestrial life (aka astrobiology), the evolution of the Solar System and its Planets, and the connections of the Sun-Earth system. Given the ambitious nature of the program and some of the wording used (“reaching a world-leading level”), it could also be seen as a declaration of intent.

For years, China has indicated its intentions to rival NASA as a major power in space. With this first-ever roadmap, it is clear that China’s long-term intentions are to replace NASA as a leader in space exploration and science.

Further Reading: CGTN, The State Council of the People’s Republic of China

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Space Force’s X-37B will Perform “Never Before-Seen Maneuvers” in Orbit

The X-37B Orbital Test Vehicle (OTV) has been shrouded in mystery since its maiden flight in 2011. Designed by Boeing and operated by the U.S. Space Force (USSF), this remotely operated, reusable space plane is designed to operate in Low-Earth Orbit (LEO), 240 to 800 km (150 to 500 mi) above the Earth, and test reusable vehicle technologies that support long-term space objectives. On December 29th, 2023, the X-37B began its seventh mission (OTV-7) and has reportedly been conducting experiments on the effects of space radiation and testing Space Domain Awareness (SDA) technologies.

As part of this mission, the X-37B will soon begin executing a series of novel maneuvers to change its orbit around Earth. These maneuvers will consist of the spacecraft brushing against Earth’s upper atmosphere to shed speed and lower its orbit without expending much fuel—a technique known as “aerobraking.” This is the first time the X-37B has performed such a maneuver, which will help it evade detection by potentially hostile nations and perform undetected low passes over Earth during future missions.

According to a statement by the USSF, this latest maneuver leverages six successful missions in LEO and decades of lessons learned from missions to the Moon and Mars. In 1997, the Mars Global Surveyor (MGS) orbiter used its solar panels as “wings” to control its passage through Mars’ tenuous upper atmosphere and lower its orbit over several months. More recently, aerobraking has been used by the Mars Odyssey in 2001, the Mars Reconnaissance Orbiter in 2006, and the ESA’s ExoMars Trace Gas Orbiter in 2017-2018.

The X-37B Orbital Test Vehicle taxiing on the flightline on March 30th, 2010, at the Astrotech facility in Titusville, Florida. Credit: USAF

“This novel and efficient series of maneuvers demonstrates the Space Force’s commitment to achieving groundbreaking innovation as it conducts national security missions in space,” said Secretary of the Air Force Frank Kendall. “This first-of-a-kind maneuver from the X-37B is an incredibly important milestone for the United States Space Force as we seek to expand our aptitude and ability to perform in this challenging domain,” added Chief of Space Operations Gen. Chance Saltzman. “The success is a testament to the dedication and perseverance of the team.”

Beyond these experiments, very little is known about the X-37B’s capabilities and purpose. However, during the Aspen Security Forum in 2019, former U.S. Air Force (USAF) Secretary Heather Wilson explained how the X-37B capabilities allow it to avoid detection, saying:

“[The X-37B is] fascinating [because it] can do an orbit that looks like an egg and, when it’s close to the Earth, it’s close enough to the atmosphere to turn where it is. Which means our adversaries don’t know – and that happens on the far side of the Earth from our adversaries – where it’s going to come up next. And we know that that drives them nuts. And I’m really glad about that.”

As Jonathan McDowell – an astronomer and astrophysicist at the Harvard-Smithsonian Center for Astrophysics – told Military.com in an interview at the time:

“[Wilson’s comments may shed light on] a previously secret orbit-related capability. The dip into the atmosphere causes a change in the timing of when it next comes overhead. So [trackers’] predictions are off, and [they] have to search for it all over again. Even a timing change makes more work for [adversaries] than just being able to use the existing orbital prediction.”

Once the aerobrake maneuver is complete, the X-37B will resume its tests and experiments until they are fulfilled. As the USSF indicated before the launch of the OTV-7 mission, these tests include operating in new orbital regimes, experimenting with future SDA technologies, and investigating the radiation effects on plant seeds provided by NASA – the “Seeds-2” experiment. The spacecraft will also eject some of its service module components in accordance with recognized standards for space debris mitigation. At this point, the vehicle will de-orbit and return to Earth as it has during its six previous missions.

Further Reading: Live Science, USSF

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Hubble and New Horizons Look at Uranus at the Same Time

Ever since the advent of space exploration we have seen some amazing images of the planets. New technology often brings with it a new perspective and we have been reminded of this again just recently with images from the Hubble Space Telescope (HST)  and New Horizons spacecraft. The two objects simultaneously imaged Uranus from different perspectives in an attempt to predict what astronomers would see when they look at exoplanets orbiting other stars. 

Uranus is the 7th planet from the Sun and is recognisable for its wonderful blue-green colour. It was discovered by William Herschel in 1781 and since then we have been probing its secrets with telescopes and space probes alike. Like the other outermost planets, Uranus is a giant ball of gas and its the presence of methane in its atmosphere that gives it the striking colour. It’s unusual among the other planets since it seems to rotate around the Sun with an axial tilt of 98 degrees so it has really quite extreme seasons. 

This zoomed-in image of Uranus, captured by Webb’s Near-Infrared Camera (NIRCam) Feb. 6, 2023, reveals stunning views of the planet’s rings. Credit: NASA, ESA, CSA, STScI IMAGE PROCESSING: Joseph DePasquale (STScI).

HST and New Horizons have recently turned their gaze on Uranus but for a somewhat unusual project, to help develop imaging techniques for exoplanets. Directly imaging the distant alien worlds is tricky simply due to their distance and often due to their proximity to the host star. It’s of great importance to be able to study them directly to be able to learn more about their nature and possible habitability. Directly imaging exoplanets often just reveals pinpoints of light so researchers have used Uranus as a ‘proxy’ exoplanet to explore new imaging methods. 

The New Horizons instrument payload that is currently doing planetary science, heliospheric measurements, and astrophysical observations. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Uranus was chosen because the majority of exoplanets are gas giants and similar in nature. It was also chosen as New Horizons was on the far side of Uranus at the time of observation placing it 10.5 billion kilometres away. From its vantage point, New Horizons would see a crescent Uranus, a phase often seen on exoplanets when they are at their furthermost point from their star. They used the Multispectral Visible Imaging Camera to grab the images with Uranus covering just a few pixels, much like an exoplanet when viewed from Earth. 

While New Horizons was taking its images, HST which was just 2.7 billion km away and with its high quality cameras could capture a fabulous amount of detail in the atmosphere. By comparing the two images, the researchers have been able to see how atmospheric features appear in the New Horizon data to help learn about exoplanet observations. The team found that both HST and New Horizons saw that the brightness did not vary as the planet rotated which revealed that the cloud features were not changing with the rotation of the planet.

This image of NASA’s Hubble Space Telescope was taken on May 19, 2009 after deployment during Servicing Mission 4. NASA

They also found that New Horizons showed exoplanets are likely to seem dimmer than predicted at partial and high phase angles. This means that a gas planet like Uranus reflects light differently at partial phases when compared to others. The results are a testimony to the wonderfully insightful approach to cracking an existing challenge in modern astronomy; The direct study of exoplanets. Over the coming years telescopes like Nancy Grace Roman Space Telescope which is due for launch in 2027 has the ability to block out light to enable direct observations of exoplanets. This latest study will help to interpret the data revealed in future studies.

Source : NASA’s Hubble, New Horizons Team Up for a Simultaneous Look at Uranus

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