Discover Terrestrial Planets That Are Less Than A Day Long in A Year Around Low-temperature Stars (Planetary Science)

A research team led by researchers at the Astrobiology Center and the University of Tokyo has observed low-temperature “ultra-short-period planets” with an orbital period of less than one day by observing with the Subaru Telescope’s near-infrared spectrometer IRD. It was discovered around a star and revealed that its internal composition consists mainly of iron and rock. The planets (TOI-1634b and TOI-1685b) found around the two low-temperature stars are both equivalent to Super-Earth (Note 1), which is about 1.5-2 times the size of the Earth, and in particular, TOI-1634b It is one of the terrestrial planets with the largest radius (1.8 Earth radius) and mass (10 Earth mass) among the ultra-short-period planets found so far. Planets of this size are on the border between rock and gas giants, especially around low-temperature stars, so how many planets have a “one year” less than the length of a day on Earth? It can be said that the most valuable celestial body was discovered in investigating whether it was formed.

Observations have revealed that about 1% of extrasolar planets (exoplanets) are planets with an orbital period of less than one day (ultra-short-period planets). It is thought that ultra-short-period planets formed in outer orbits may have moved to inner orbits due to interactions with other planets, etc., in order to understand the formation of various planets. , A rare and important celestial body.

Most of the ultra-short-period planets observed so far are small planets with a radius of 1.5 times or less that of the Earth, and it is known that their internal composition is similar to that of the Earth, which is mainly composed of iron and rocks. However, most of the ultra-short-period planets scrutinized in this way are known only around sun-like stars (solar stars), and there are only a few observations around low-temperature, small-mass stars. is. Low-temperature stars are known to have multiple small planets, so ultra-short-period planets may also be present. A closer look at the frequency and characteristics of ultrashort-period planets around low-temperature stars is expected to give a general understanding of the origins of ultra-short-period planets.

The research team focused on two low-temperature stars TOI-1634 and TOI-1685 with transit planet candidates (Note 2) detected by NASA’s Transiting Exoplanet Exploration Satellite “TESS”. .. The mass of these stars is only about half that of the Sun. Independent analysis of TESS data and follow-up observation of transit using the MuSCAT series of multicolor simultaneous imaging cameras (Note 3), followed by spectroscopic observation using the Subaru Telescope’s infrared spectroscope IRD (InfraRed Doppler). Did. The IRD is a spectroscope that accurately measures the radial velocity of a star (radial velocity), and is a unique observation device optimized for observing low-temperature stars that appear brighter with infrared rays than visible light.

As a result of detailed analysis of the radial velocities observed by IRD, the actual ultra-short-period planets around TOI-1634 and TOI-1685 were 0.989 days (TOI-1634b) and 0.669 days (TOI-1685b), respectively. It was confirmed that it revolves in the cycle of. Furthermore, from the amplitude of the change in radial velocity, it became clear that TOI-1634b and TOI-1685b have about 10 times and about 3.4 times the mass of the earth, respectively (Note 4). When the composition of the planet was theoretically estimated based on this planet mass and the planet radius (TOI-1634b is about 1.8 earth radius, TOI-1685b is about 1.5 earth radius) obtained from transit observation, which planet It was found that, like the earth, has an internal composition mainly centered on iron and rocks (Fig. 2). Two planetary systems have been discovered in which Super-Earth, which has a composition similar to that of the Earth, revolves in the immediate vicinity of low-temperature, small-mass stars.

Discovering terrestrial planets with a "one year" length of less than one day around low-temperature stars Figure 2
Figure 2: Distribution of mass and radius of planets with less than 3 earth radii among the exoplanets found so far. Previously known ultrashort-period planets are shown in blue or purple, and the two newly discovered ultra-short-period planets are shown in red (blue is around the sun-shaped stars, purple is around the cold M-type dwarfs). Ultra-short-period planet). Gray dots are planets with an orbital period of 1 day or more. The relationship between the mass and radius of each planet’s internal composition by theoretical calculation is shown by a different color curve, and all the ultra-short-period planets shown are the composition of the earth (mass ratio 67.5% rock, 32.5% iron). ) And you can see that it is almost the same. On the other hand, the planets with a large radius (gray) distributed in the upper right of the figure can be explained by a model with a hydrogen atmosphere on the outside like Jupiter and Neptune. (Credit: Astrobiology Center)

TOI-1634b is one of the planets with the largest radius and mass among the ultra-short-period planets confirmed to have an internal composition similar to that of the Earth, and such planets are around stars that are much lighter than the Sun. It is very interesting to find in. From the “mass-radius” relationship (Fig. 2), it was also found that there is no thick hydrogen atmosphere on both planets. On both planets, where no protoplanetary atmosphere of gas from the protoplanetary disk is left, a secondary atmosphere of gas released by the planets may be formed. It is also an interesting observation target for studying how the atmosphere of terrestrial planets that orbit the immediate vicinity of stars evolves.

Both planetary systems are located relatively close to the Earth about 100 light-years, and are particularly bright among low-temperature stars with ultra-short-period planets, making them promising observation candidates for next-generation telescopes. The lead author of the paper, Assistant Professor Teruyuki Hirano (National Institute of Natural Sciences, Astrobiology Center / National Institute of Natural Sciences, Hawaii Observatory) said, “In the future, we will observe the planetary system found in this research with the James Webb Space Telescope (JWST). By investigating the planetary atmosphere and detailed orbits, it is expected that the origin of the still mysterious ultra-short-period planets will be elucidated. Also, the planetary candidate celestial bodies identified by TESS will be intensively tracked by IRD. The observing project is still underway and many unique planets should be identified in the IRD in a year or two, “he said.


This research result was published in the American astronomy journal “Astronomical Journal” (September 23, 2021) (Hirano et al. ” Two Bright M Dwarfs Hosting Ultra-Short-Period Super-Earths with Earth” -like Compositions “).


(Note 1) “Super Earth” is a planet larger than the Earth, and refers to an exoplanet whose mass is about 10 times or less that of the Earth and whose diameter is about 2 times or less that of the Earth. Since there are no planets of such weight and size in the solar system, observations of exoplanets have revealed that such planets exist for the first time.

(Note 2) “Transit” is a phenomenon in which a star appears to be dark periodically because the planet passes in front of the star. The exoplanet system in which transit is observed is called the transit planetary system. In transit exploration such as TESS, many transit-like dimmings are detected by large-scale photometric monitor observations, including false detections by “eclipsing binaries”. It is confirmed that the “transit planet candidate” detected by TESS is a real transit planet for the first time by performing follow-up observations using other telescopes.

(Note 3) Multicolor simultaneous imaging cameras mounted on the 188 cm telescope in Okayama Prefecture, the 1.52 m telescope at the Teide Observatory in Tenerife, Spain, and the 2 m telescope at the Haleakala Observatory in Maui, USA, MuSCAT, MuSCAT2 , MuSCAT3 was used for follow-up observation of transit. For all planets, this follow-up observation accurately determined parameters such as the orbital period and planetary radius that were tentatively obtained by TESS.

(Note 4) If there are planets around the star, the star will fluctuate slightly due to the influence of the planet’s gravity. The radial velocity method captures this fluctuation as a periodic change in the radial velocity of a star. The larger the mass of the planet, the larger the amplitude of the change in radial velocity. The masses of the two planets found were determined by follow-up observations by the IRD.

Featured image: An image illustration comparing the sizes of the terrestrial planets discovered in this study. TOI-1685b is 1.5 times the diameter of the earth and TOI-1684b is 1.8 times the diameter. Both planets are surrounded by stars that are cooler than the Sun, so they are illuminated by reddish light. (Credit: National Institute of Natural Sciences Astrobiology Center)


Provided by Subaru Telescope

Planets Gone Rogue Could Sustain Life, According to Recent Study (Planetary Science)

A rogue planet is an interstellar object of planetary mass without a host planetary system. As they freely roam around space, could they be fertile nurseries for life?

A Florida Tech scientist believes it’s possible based on extensive research he has undertaken over the past several years.

In research highlighted this summer in Discover Magazine, university astrobiologist Manasvi Lingam (along with Harvard researcher Avi Loeb) studied how life might survive on a rogue planet via oceans prevalent underneath a thick layer of ice. The cold of interstellar space would be too much for the oceans to remain entirely liquid, but the researchers believe any putative biospheres would be protected from the cold via the ice layer, and the planet’s core would heat the planet from the inside. Underneath the ice would potentially exist Earth-like oceans that could support life.

The possibilities for rogue planets facilitating life are of deep interest to Lingam as more planets are being discovered. He noted that for every solar system discovered (each of which contains a handful of terrestrial planets), there are approximately 30-40 rogue planets traveling in the cold expanses of interstellar space. The nearest exoplanet to Earth is therefore expected to be one of these rogue planets.

“We normally think of planets bound to stars, such as Mars, that could support life, but in reality, these types of life-supporting planets could just be floating out there in the vast void of space with rich biospheres,” he said.

The next steps in the research are to do experiments on Earth to ascertain under what extreme conditions life could survive, such as low temperatures or low pressure. A way of doing this is to analyze microbes that would not need sunlight, thereby building on previous research that has conclusively shown that more microbes exist that don’t require sunlight than those that do. Another direction that merits future research is to look at rogue planets as they enter our solar system and research the planet’s conditions to see if it would facilitate life.

Lingam noted that technology would have to advance by only a modest amount to make traveling to these planets – if they are in our solar system – easier. He has published a paper on this subject, detailing how missions to these interstellar interlopers are feasible. And this subject is also covered in his recent graduate-level textbook on astrobiology, Life in the Cosmos, published by Harvard University Press in July 2021.

“You might be able to get to a rogue planet in a few decades, and, rather than looking for other planets around other stars, this might be the best chance to study these planets,” Lingam said. “Through a combination of gravity assists and suitable propulsion systems, you could reach the rogue planet in 20 years or so. Once you have a probe on the surface, you can beam the data back and it would probably take a few months to learn what it looks like on the surface.”


Provided by Florida Tech

Study Finds Photosynthesis in Venus’ Clouds Could Support Life (Planetary Science)

New data analysis has found that the sunlight filtering through Venus’ clouds could support Earth-like photosynthesis in the cloud layers and that chemical conditions are potentially amenable to the growth of microorganisms. 

Biochemistry Professor Rakesh Mogul is the lead author of the study, Potential for Phototrophy in Venus’ Clouds, published online this weekin the journal Astrobiology’s October 2021 special issue focused on the possible suitability of Venus’ clouds for microbial life, and constraints that may prohibit life.

According to Mogul and his team, which includes Michael Pasillas (’21, M.S.), photosynthesis could occur round-the-clock in Venus’ clouds with the middle and lower clouds receiving solar energy similar to the Earth’s surface. Much like on Earth, hypothetical phototrophs in Venus’ clouds would have access to solar energy during the day.

In a fascinating twist, the team found that photosynthesis may continue through the night due to thermal or infrared energy originating from the surface and the atmosphere. In this habitat, light energy would be available from both above and below the clouds, which could provide photosynthetic microorganisms ample opportunities to diversify across the cloud layers. Both the solar and thermal radiation in Venus’ clouds possess wavelengths of light that can be absorbed by the photosynthetic pigments found on Earth.

The study also found that after filtering through the Venusian atmosphere, scattering and absorption scrubs the sunlight of much of the ultraviolet radiation (UV) that is harmful to life, providing a benefit like Earth’s ozone layer.

Yeon Joo Lee, a co-author of the study, used a radiative transfer model to show that the present-day middle and lower cloud layers above Venus receive significantly less UV, 80-90% less flux in the UV-A when compared to Earth’s surface, and are essentially depleted of radiation in the UV-B and UV-C, which represent the most harmful components of the UV. 

To gauge the nighttime photosynthetic potential via Venus’ thermal energy, Mogul and his team compared the photon fluxes rising from Venus’ hot atmosphere and surface to the photon fluxes measured within low-light phototrophic habitats on Earth – hydrothermal vents in the East Pacific Rise, where geothermal emissions are reported to support phototrophy at depths of 2400 meters, and the Black Sea, where solar powered phototrophs are found at depths of 120 meters.  These comparisons showed that photon fluxes from Venus’ atmosphere and surface exceed the fluxes measured in these low-light phototrophic environments on Earth. 

While a recent report by Hallsworth et al. 2021, concluded that Venus’ clouds were too dry to support terrestrial life, Mogul and his team found that the chemical conditions of Venus’ clouds could be partly composed of neutralized forms of sulfuric acid, such as ammonium bisulfate. These chemical conditions would exhibit dramatically higher water activities when compared to Hallsworth’s calculations and much lower acidities when compared to current models for Venus. 

“Our study provides tangible support for the potential for phototrophy and/or chemotrophy by microorganisms in Venus’ clouds,” said Mogul. “The acidity and water activity levels potentially fall within an acceptable range for microbial growth on Earth, while the constant illumination with limited UV suggests that Venus’ clouds could be hospitable for life. We believe that Venus’ clouds would make a great target for habitability or life detection missions, like those currently planned for Mars and Europa.”

Pasillas, who recently graduated with a M.S. focused on chemical education from the Chemistry & Biochemistry Department, began his work on the study in a graduate seminar course (CHM 5500) taught by Mogul. Students in the class worked on small literature projects and were offered the opportunity to continue with the research. Pasillas ultimately worked on the assessments of acidity and included the work in his thesis. He is currently teaching chemistry at Mt. San Antonio College.

The co-authors of the study are Sanjay S. Limaye (University of Wisconsin, Madison), Yeon Joo Lee (Technische Universitat Berlin, Berlin, Germany) and Pasillas (M.S., chemistry ‘21).

Featured image: Night on Venus in Infrared from Orbiting Akatsuki. Source: ISAS, JAXA


Provided by CPP

Investigating the Potential For Life Around the Galaxy’s Smallest Stars (Planetary Science)

New telescope will see planetary neighbors’ atmospheres

hen the world’s most powerful telescope launches into space this year, scientists will learn whether Earth-sized planets in our ‘solar neighborhood’ have a key prerequisite for life — an atmosphere.

James Webb Space Telescope
Artist conception of the James Webb Space Telescope, successor to the Hubble Space Telescope. (NASA)

These planets orbit an M-dwarf, the smallest and most common type of star in the galaxy. Scientists do not currently know how common it is for Earth-like planets around this type of star to have characteristics that would make them habitable.

“As a starting place, it is important to know whether small, rocky planets orbiting M-dwarfs have atmospheres,” said Daria Pidhorodetska, a doctoral student in UC Riverside’s Department of Earth and Planetary Sciences. “If so, it opens up our search for life outside our solar system.”

To help fill this gap in understanding, Pidhorodetska and her team studied whether the soon-to-launch James Webb Space Telescope, or the currently-in-orbit Hubble Space Telescope, are capable of detecting atmospheres on these planets. They also modeled the types of atmospheres likely to be found, if they exist, and how they could be distinguished from each other. The study has now been published in the Astronomical Journal. 

Study co-authors include astrobiologists Edward Schwieterman and Stephen Kane from UCR, as well as scientists from Johns Hopkins University, NASA’s Goddard Space Flight Center, Cornell University and the University of Chicago.

Artist rendering of a red dwarf or M star, with three exoplanets orbiting. About 75 percent of all stars in the sky are the cooler, smaller red dwarfs. IMAGE CREDIT: NASA.
Artist rendering of an M-dwarf star, with three exoplanets orbiting. About 75 percent of all stars in the sky are the cooler, smaller red dwarfs. (NASA)

The star at the center of the study is an M-dwarf called L 98-59, which measures only 8% of our sun’s mass. Though small, it is only 35 light years from Earth. It’s brightness and relative closeness make it an ideal target for observation. 

Shortly after they form, M-dwarfs go through a phase in which they can shine two orders of magnitude brighter than normal. Strong ultraviolet radiation during this phase has the potential to dry out their orbiting planets, evaporating any water from the surface and destroying many gases in the atmosphere. 

“We wanted to know if the ablation was complete in the case of the two rocky planets, or if those terrestrial worlds were able to replenish their atmospheres,” Pidhorodetska said. 

The researchers modeled four different atmospheric scenarios: one in which the L 98-59 worlds are dominated by water, one in which the atmosphere is mainly composed of hydrogen, a Venus-like carbon dioxide atmosphere, and one in which the hydrogen in the atmosphere escaped into space, leaving behind only oxygen and ozone. 

They found that the two telescopes could offer complementary information using transit observations, which measure a dip in light that occurs as a planet passes in front of its star. The L 98-59 planets are much closer to their star than Earth is to the sun. They complete their orbits in less than a week, making transit observations by telescope faster and more cost effective than observing other systems in which the planets are farther from their stars. 

“It would only take a few transits with Hubble to detect or rule out a hydrogen- or steam-dominated atmosphere without clouds,” Schwieterman said. “With as few as 20 transits, Webb would allow us to characterize gases in heavy carbon dioxide or oxygen-dominated atmospheres.”

Of the four atmospheric scenarios the researchers considered, Pidhorodetska said the dried-out oxygen-dominated atmosphere is the most likely. 

“The amount of radiation these planets are getting at that distance from the star is intense,” she said.

Though they may not have atmospheres that lend themselves to life today, these planets can offer an important glimpse into what might happen to Earth under different conditions, and what might be possible on Earth-like worlds elsewhere in the galaxy. 

The L 98-59 system was only discovered in 2019, and Pidhorodetska said she is excited to get more information about it when Webb is launched later this year. 

“We’re on the precipice of revealing the secrets of a star system that was hidden until very recently,” Pidhorodetska said.


Provided by UCR Riverside

How To Detect And Confirm The Presence Of Antistars? (Cosmology)

In the recent paper, Postnov and colleagues proposed an idea to detect electromagnetic signal from annihilation in outer layers of antistars. Their idea is to search for antistars in the Galaxy through X-rays in the ∼ (1–10) keV energy band. The reason is, prior to annihilation, protons and antiprotons could form atomic-type excited bound states (‘protonium’, Pn), similar to 𝑒+𝑒¯-positronium (Ps) atoms, and in the process of de-excitation of protonium, an antistar could emit not only ∼ 100-MeV gamma-rays but a noticeable flux of X-rays with energies in the keV range. Their study recently appeared in Arxiv.

Antistars are objects that could have form from smaller high baryonic number (HBB). They were created in the very early universe after the QCD phase transition at 𝑇 ∼ 100 MeV & should also populate the galactic halo. Such stars are not only too old, but also they are moving very fast, and have a highly unusual chemical content. Present observations also favored the possibility of their existence.

Now, Postnov and colleagues explored the possibility that, when antistars interact with interstellar medium (ISM) gas it can give rise to excited protonium atoms. Formation of these atoms takes place most effectively during interaction of protons with neutral (or molecular) antimatter. This can happen if an antistar has a noticeable wind mass-loss.

“These (protonium) atoms rapidly cascade down to low levels prior to annihilation giving rise to a series of narrow lines which can be associated with the hadronic annihilation gamma-ray emission.”

— wrote authors of the study.

They have also shown that these protonium atoms cascade to the 2p-state producing mostly L (Balmer) 3d-2p X-rays around ∼ 1.7 keV line before the 𝑝𝑝¯ hadronic annihilation.

While, antistars formed in higher HBBs should have an enhanced helium abundance. Therefore, the 4.86 keV M (4-3) and 11.13 L (3-2) narrow X-ray lines from cascade transitions in ⁴He𝑝¯ atoms can also be associated with gamma-rays from hadronic annihilations.

“These lines are interesting from the observational point of view because the protonium 3d-2p transition line energy 1.73 keV is close to the Si K-shell complex lines, which could hamper its disentangling from the background.”

— wrote authors of the study.

Finally, it has been suggested, these lines can be probed in dedicated observations by forthcoming sensitive X-ray spectroscopic missions XRISM and Athena and in wide-field X-ray surveys like SRG/eROSITA all-sky survey.


Reference: Bondar et al., “X-ray signature of antistars in the Galaxy”, pp. 1-10, 2021.
arXiv:2109.12699


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