Showing posts with label Gliese 486b. Show all posts
Showing posts with label Gliese 486b. Show all posts

Thursday, November 28, 2024

Charting the Cosmic Shoreline: Which Planets Have Atmospheres?

Illustration of an M-dwarf star covered in sunspots and emitting a stellar flare. Its planet is subjected to fierce stellar activity that strips away the planet's atmosphere. Credit: NASA/ESA/STScI/G. Bacon

Which of the nearly 6,000 known exoplanets have atmospheres? With help from JWST, astronomers are inching closer to an answer, and new observations of a super-Earth planet around a low-mass star help to define the dividing line between planets with atmospheres and planets without.

Cartoon showing the geometry of a transit observation and a secondary eclipse observation.
Credit: AAS Nova/Kerry Hensley

How to Find an Atmosphere

With the number of known exoplanets growing steadily larger, a major challenge for astronomers is deciding how to allocate limited telescope time to study these planets further. Rocky planets with atmospheres make promising targets, but it’s not obvious which exoplanets should have atmospheres. Taking cues from the planets in our solar system and the subset of exoplanets that have been studied in detail, researchers have defined the concept of the cosmic shoreline, which separates planets with atmospheres from planets without on the basis of escape velocity — related to a planet’s mass and size — and the amount of starlight the planet receives.

While simple in concept, charting the cosmic shoreline is difficult, especially for planets circling M dwarfs: the smallest, coolest, and most common type of star. M dwarfs are notorious for their extreme space weather, which can strip away a planet’s atmosphere over billions of years. To learn more about the exact position of the cosmic shoreline and to guide our observations of M-dwarf exoplanets, researchers must search for atmospheres on planets subjected to the fierce conditions of an M-dwarf host star.


Best-fitting bare surface (top) and atmosphere (middle) models. The bottom panel shows poorly fitting models.
Credit: Mansfield et al. 2024

A Promising Planet

Discovered by the Transiting Exoplanet Survey Satellite (TESS), Gliese 486b (Gl 486b or GJ 486b) is a super-Earth exoplanet with a radius of 1.29 Earth radii and a mass of 2.77 Earth masses. Its host star is a 6.6-billion-year-old M dwarf that is known to explode with high-energy stellar flares. At just 26 light-years away, Gl 486b is one of the closest transiting terrestrial exoplanets known.

Last year, researchers published an investigation of Gl 486b’s atmosphere, finding that JWST transmission spectra suggested either a water-rich atmosphere or no atmosphere at all. If there is no atmosphere, the observed signal from water vapor must have come from cool regions on the host star rather than from the planet’s atmosphere.

Recently, Megan Weiner Mansfield (Steward Observatory; Arizona State University) and collaborators used JWST to collect secondary eclipse observations of Gl 486b, watching as the planet passed behind its host star. Secondary eclipse observations show the thermal glow of the planet and starlight reflected from its surface. Coupling the secondary eclipse observations with previously collected JWST and TESS data, the team found that the planet’s dayside temperature is a scorching 865K. This high temperature suggests that Gl 486b has either a thin atmosphere or no atmosphere at all, since a thick atmosphere would redistribute the heat and lower the dayside temperature.

Location of Gl 486b relative to the approximate cosmic shoreline.
Credit: Mansfield et al. 2024

Atmosphere Likely Lacking

With these constraints in hand, Mansfield’s team used forward modeling to explore the types of atmospheres that could be present. They found that a planet with no atmosphere provided the best fit to the data, but a thin atmosphere was also acceptable, as long as it contained only a small amount of water or carbon dioxide.

Given the realities of 6.6 billion years spent around an active M-dwarf star, the team concluded that Gl 486b is unlikely to have an atmosphere. In addition to weighing in on the likelihood of Gl 486b having a water-rich atmosphere, the team also achieved the most precise measurement yet of a planet’s dayside temperature, constraining the temperature to within just 14K.

By Kerry Hensley

Citation

“No Thick Atmosphere on the Terrestrial Exoplanet Gl 486b,” Megan Weiner Mansfield et al 2024 ApJL 975 L22. doi:10.3847/2041-8213/ad8161


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Monday, March 08, 2021

A blazing nearby super-Earth

Artistic impression of the surface of the newly discovered hot super-Earth Gliese 486b. With a temperature of about 700 Kelvin (430 °C), the astronomers of the CARMENES collaboration expect a Venus-like hot and dry landscape interspersed with glowing lava rivers. Gliese 486b possible has a tenuous atmosphere. © Image: RenderArea

The diagram provides an estimate of the interior compositions of selected exoplanets based on their masses and radii in Earth units. The red marker represents Gliese 486b, and orange symbols depict planets around cool stars like Gliese 486. Grey dots show planets hosted by hotter stars. The coloured curves indicate the theoretical mass-radius relationships for pure water at 700 Kelvin (blue), for the mineral enstatite (orange), for the Earth (green), and pure iron (red). For comparison, the diagram also highlights Venus and the Earth.  © Image: Trifonov et al./MPIA graphics department 
 

The graph illustrates the orbit of a transiting rocky exoplanet like Gliese 486b around its host star. During transit, the planet obscures the stellar disk. Simultaneously, a tiny portion of the starlight passes through the planet’s atmospheric layer. While Gliese 486b continues to orbit, parts of the illuminated hemisphere become visible like lunar phases until the planet vanishes behind the star.  © Image: MPIA graphics department

During the recent two and a half decades, astronomers have discovered thousands of exoplanets made of gas, ice and rock. Only a few of them are Earth-like. However, probing their atmospheres with the currently available instrumentation is challenging at best. Now, astronomers of the CARMENES consortium have published a new study, led by Trifon Trifonov from the Max Planck Institute for Astronomy, which reports the discovery of a hot rocky super-Earth orbiting the nearby red dwarf star Gliese 486. Despite its small separation from the parent star, the planet designated Gliese 486b possibly has retained a part of its original atmosphere. Therefore, Gliese 486b is uniquely suited to examine its atmosphere and interior with the next generation of space-borne and ground-based telescopes. The results are published in the journal Science today.

With the advent of efficient exoplanet-hunting facilities, the numbers of newly discovered worlds outside the Solar System quickly rose to thousands. By combining different observing techniques, astronomers have determined planetary masses, sizes, and even bulk densities, allowing them to estimate their internal composition. The next goal to fully characterize those exoplanets similar to Earth by studying their atmospheres is much more challenging. Especially for rocky planets like Earth, any such atmosphere consists of a thin layer, if it exists at all. As a result, many current atmospheric models of rocky planets remain untested.

Planetary atmospheres must meet specific prerequisites to observe them with next-generation observatories. At a distance of only 26 light-years, scientists of the CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs) consortium now have found a planet orbiting the red dwarf star Gliese 486 that perfectly satisfies these specifications for rocky planets. The newly discovered planet designated Gliese 486b is a super-Earth with a mass 2.8 times that of our home planet. It is also 30% bigger than Earth. The scientists employed both transit photometry and radial velocity spectroscopy to obtain their results.

“The proximity of this exoplanet is exciting because it will be possible to study it in more detail with powerful telescopes such as the upcoming James Webb Space Telescope and the future Extremely Large Telescopes,” Trifon Trifonov explains. He is a planetary scientist at the Max Planck Institute for Astronomy (MPIA) and lead author of the article that features this discovery.

By calculating the planet’s mean density from the mass and radius measurements, its composition appears similar to Venus and Earth, including a metallic core. Anyone standing on Gliese 486b would feel a gravitational pull that is 70% stronger than what we experience on our world.

Gliese 486b revolves around its host star on a circular trajectory within 1.5 days and at a distance of 2.5 million kilometres. One rotation takes the same amount of time, so one side always faces the star. Although the star Gliese 486 is much fainter and cooler than the Sun, the irradiation is so intense that the planet’s surface heats up to at least 700 Kelvin (approx. 430 °C). In this sense, Gliese 486b’s surface probably looks more like Venus than Earth, with a hot and dry landscape interspersed with glowing lava rivers. However, unlike Venus, Gliese 486b possibly only has a tenuous atmosphere if any. Model calculations may be consistent with both scenarios because stellar irradiation tends to evaporate atmospheres. At the same time, the planet’s gravity helps to retain it. Figuring out the balance of those contributions is difficult.

“The discovery of Gliese 486b was a stroke of luck. A hundred degrees hotter and the planet’s entire surface would be lava. Its atmosphere would consist of vapourised rocks,” José A. Caballero of the Centro de Astrobiología (CSIC-INTA, Spain) and co-author of the paper concludes. “On the other hand, if Gliese 486b were a hundred degrees colder, it would have been unsuitable for follow-up observations.”

The future measurements that the CARMENES team have in mind exploit the orbital orientation, which causes Gliese 486b to cross the surface of the host star from our point of view. Whenever this happens, a tiny fraction of the stellar light shines through the thin atmospheric layer before it reaches Earth. The various compounds absorb light at specific wavelengths, leaving their footprint in the signal. By using spectrographs, the astronomers split up the light according to wavelengths and look for absorption features to derive the atmospheric composition and dynamics. This method is also known as transit spectroscopy.

A second spectroscopic measurement, called emission spectroscopy, is planned when parts of the illuminated hemisphere become visible like lunar phases during Gliese 486b’s orbit until it vanishes behind the star. The spectrum contains information on the bright, hot planetary surface.

“We can hardly wait for the new telescopes to become available,” Trifonov admits. “The results will help us to understand how well rocky planets can hold their atmospheres, what they are made of and how they influence the energy distribution on the planets.”

Both Trifonov and Caballero collaborate in the CARMENES project, whose consortium comprises eleven research institutions in Spain and Germany. Its purpose is to monitor some 350 red dwarf stars for signs of low-mass planets using a spectrograph mounted at the 3.5 m Calar Alto telescope (Spain). This study includes additional spectroscopic measurements to infer Gliese 486b’s mass. The scientists obtained observations with the MAROON-X instrument at the 8.1 m Gemini North telescope (USA) and retrieved archival data from the 10 m Keck telescope (USA) and the ESO 3.6 m telescope (Chile).

Photometric observations to derive the planet’s size stem from the TESS (Transiting Exoplanet Survey Satellite) spacecraft (NASA, USA), the MuSCAT2 (Multicolour Simultaneous Camera for studying Atmospheres of Transiting exoplanets 2) instrument mounted at the 1.52 m Telescopio Carlos Sánchez at Observatorio del Teide (Spain), and the LCOGT (Las Cumbres Observatory Global Telescope), among others.

Source: Max Planck Institute for Astronomy

Background information

The team was composed of T. Trifonov (Max-Planck-Institut für Astronomie [MPIA]), J. A. Caballero (Centro de Astrobiología [CAB]), J. C. Morales (Institut de Ciències de l'Espai [ICE] and Institut d’Estudis Espacials de Catalunya [IEEC-CSIC]), A. Seifahrt (The University of Chicago), I. Ribas (ICE/IEEC-CSIC), A. Reiners (Institut für Astrophysik, Georg-August-Universität Göttingen [Uni Göttingen]), J. L. Bean (The University of Chicago), R. Luque (Instituto de Astrofísica de Canarias [IAC] and Universidad de La Laguna [ULL]), H. Parviainen (IAC/ULL), E. Pallé (IAC/ULL), S. Stock (Zentrum für Astronomie der Universität Heidelberg [ZAH]) , M. Zechmeister (The University of Chicago), P. J. Amado (Instituto de Astrofísica de Andalucía [IAA-CSIC]), G. Anglada-Escudé (ICE/IEEC-CSIC), M. Azzaro (Centro Astronómico Hispano-Alemán [CAHA]), T. Barclay (NASA Goddard Space Flight Center, and University of Maryland), V. J. S. Béjar (IAC/ULL), P. Bluhm (ZAH), N. Casasayas-Barris (IAC/ULL), C. Cifuentes (CAB), K. A. Collins (Center for Astrophysics, Harvard & Smithsonian [CfA]), K. I. Collins (George Mason University), M. Cortés-Contreras (CAB), J. de Leon (The University of Tokyo), S. Dreizler (Uni Göttingen), C. D. Dressing (University of California at Berkeley), E. Esparza-Borges (IAC/ULL), N. Espinoza (Space Telescope Science Institute), M. Fausnaugh (Massachusetts Institute of Technology [MIT]), A. Fukui (The University of Tokyo), A. P. Hatzes (Thüringer Landessternwarte Tautenburg), C. Hellier (Keele University), Th. Henning (MPIA), C. E. Henze (NASA Ames Research Center), E. Herrero (ICE/IEEC-CSIC), S. V. Jeffers (Uni Göttingen), J. M. Jenkins (NASA Ames Research Center), E. L. N. Jensen (Swarthmore College), A. Kaminski (ZAH), D. Kasper (The University of Chicago), D. Kossakowski (MPIA), M. Kürster (MPIA), M.Lafarga (ICE/IEEC-CSIC), D. W. Latham (CfA), A. W. Mann (University of North Carolina at Chapel Hill,), K. Molaverdikhani (ZAH), D. Montes (Departamento de Física de la Tierra y Astrofísica & IPARCOS-UCM), B. T. Montet (University of New South Wales), F. Murgas (IAC and Departamento de Astrofísica, ULL), N. Narita (The University of Tokyo, Japan Science and Technology Agency, Astrobiology Center, and IAC), M. Oshagh (IAC and Departamento de Astrofísica, ULL), V. M.Passegger (Universität Hamburg and University of Oklahoma,), D. Pollacco (University of Warwick), S. N. Quinn (CfA), A. Quirrenbach (ZAH), G. R. Ricker (MIT), C. Rodríguez López (IAA), J. Sanz-Forcada (CAB), R. P. Schwarz (Patashnick Voorheesville Observatory), A. Schweitzer (Universität Hamburg), S. Seager (MIT), A. Shporer (MIT), M. Stangret (IAC/ULL), J. Stürmer (Universität Heidelberg), T. G. Tan (MIT), P. Tenenbaum (MIT), J. D. Twicken (SETI Institute and NASA Ames Research), R. Vanderspek (MIT), and J. N. Winn (Princeton University).


Contact

Dr. Trifon Trifonov
Phone:+49 6221 528-443 
Max Planck Institute for Astronomy, Heidelberg

Dr. Markus Nielbock
span style="color: #f1c232;">Press and public relations officer
Phone:+49 6221 528-134
Max Planck Institute for Astronomy, Heidelberg
Mobile: +49 15678 747326


Original Aplication
 
1. T. Trifonov, J. A. Caballero, J. C. Morales et al.
A nearby transiting rocky exoplanet that is suitable for atmospheric investigation
Science (2021)
Source
 


Video  -  A journey to Gliese 486b

This virtual journey to Gliese 486b begins with its position in the night sky. After focusing on the parent star Gliese 486b, the film depicts the measurements. Finally, we fly to the exoplanet Gliese 486b and explore its possible surface, which probably resembles Venus, with a hot and dry landscape interspersed with glowing lava flows. 
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