Super-Earth Ross 508b Skims Red Dwarf’s Habitable Zone

Super-Earth Ross 508b Skims Red Dwarf's Habitable Zone

Figure 1: Schematic diagram of the newly discovered planetary system around Ross 508. The green zone represents the habitable zone (HZ) where liquid water can exist on the planet’s surface. The orbits of the planets are shown as blue lines. For more than half of its orbit, the planet is projected to be located lower than HZ (solid line) and within HZ (dashed line) for the rest of its orbit. credit: Astrobiology Center

The first exoplanet has been discovered by the Subaru Strategic Program using the Infrared Spectrograph IRD on the Subaru Telescope (IRD-SSP). This planet, Ross 508b, is a super-Earth, with a mass about four times that of Earth and located near the habitable zone. Such a planet may be able to retain water on its surface, and would be an important target for future observations to verify the possibility of life around low-mass stars.

Research on exoplanets, which has made great progress in recent years since the discovery of a giant planet around a star similar to our Sun, is now focusing on red dwarfs, which have less mass than our Sun. Red dwarfs, which make up three-quarters of the stars in our galaxy and are present in large numbers around our solar system, are excellent targets for finding exoplanets in our neighborhood. The discovery of such nearby exoplanets, along with detailed observations of their atmospheres and surface layers, will allow us to discuss the presence or absence of life in environments that are very different from our solar system.

However, due to surface temperatures of less than 4,000 degrees, red dwarfs are very rare in visible light. Previous planet searches using visible light spectrometers have discovered only a few planets around very nearby red dwarfs, such as Proxima Centauri b. In particular, red dwarfs with surface temperatures below 3,000 degrees (late-type red dwarfs) have not been systematically searched for planets. The transit method, which detects changes in stellar brightness as a planet passes in front of a star, does not require as many photons as the spectroscopic Doppler method, so planets around red dwarfs using the transit method. The search has been progressing in recent years. , Transit with TESS (Transiting Exoplanet Survey Satellite) could detect planet search terrestrial planet Around relatively heavy red dwarfs (early type red dwarfs).

Although red dwarfs are important targets for studying life in the universe, they are difficult to observe because they are so low in visible light. To address the difficulties involved in spectroscopic observations of red dwarfs, a planet discovery using a high-precision spectrograph in the infrared, where red dwarfs are relatively bright, has been long-awaited. For example, the luminosity of the Sun as seen from 30 light years away is magnitude five in visible light and magnitude three in infrared light. On the other hand, the lightest late red dwarfs are very faint in visible light at magnitude 19, but relatively bright in the infrared at magnitude 11.

The Astrobiology Center in Japan has successfully developed the IRD (Infrared Doppler Instrument), the world’s first high-precision infrared spectrograph for an 8-meter class telescope. The IRD on the Subaru Telescope can detect minute tremors in the velocity of a star, about the speed of a person’s movement.

The transit method can only detect planets whose orbits are along the line of sight, while the Doppler method can detect planets regardless of their orientation with respect to the celestial plane. It is also an important way that it can determine the “mass” of a planet.

The IRD Subaru Strategic Program (IRD-SSP) began in 2019 to search for planets around late-type red dwarfs. This is the first systematic planetary discovery around late-type red dwarfs and an international project involving about 100 domestic and international researchers. During the first two years, screening observations were made to find “stable” red dwarfs with low noise, where minor planets could also be detected. Red dwarfs have high surface activity, such as flares, and this surface activity can cause changes in the line-of-sight velocity of the star, even when no planets are present. Therefore, only stable red dwarfs with low surface activity are targets in the search for small Earth-like planets.

Currently, the project is in the intensive observation phase of about 50 promising late-type red dwarfs, which were carefully selected through screening.

Super-Earth Ross 508b Skims Red Dwarf's Habitable Zone

Figure 2: Periodic variation in the line-of-sight velocity of the star Ross 508 as observed by the IRD. It wraps around the orbital period of the planet Ross 508b (10.77 days). The Ross 508’s line-of-sight velocity change is less than 4 meters per second, indicating that the IRD captured a very small wobble that is slower than the one running. The red curve is best suited for observations and its deviation from the sinusoidal curve indicates that the planet’s orbit is most likely elliptical. credit: Harakawa et al. 2022

The first exoplanet discovered by IRD-SSP is located around a red dwarf star named Ross 508, about 37 light-years from Earth, which is one-fifth the mass of the Sun. It is the first exoplanet discovered by systematic search using an infrared spectrometer.

To confirm that Ross 508’s periodic fluctuations are in fact caused by a planet, the IRD-SSP team identified several indicators of stellar activity that can generate false-positives of a planet (e.g. for stellar brightness and the shape of some emission lines) and showed that the periods of these indicators differ markedly from the observed planetary periods. This is a more difficult task than using the Doppler method to confirm planetary candidates. transit methodBut it is an essential method for detecting non-transiting planets.

The minimum mass of this planet, named Ross 508b, is only four times the mass of Earth. Its average distance from its central star is 0.05 times the Earth-Sun distance, and it lies at the inner edge of habitable zone, Interestingly, the planet is likely to have an elliptical orbit, in which case it would cross into the habitable zone with an orbital period of about 11 days (Figures 1 and 2).

Planets in the habitable zone can retain water on their surfaces and harbor life. Ross 508b will be an important target for future observations to verify the possibility of habitable planets around red dwarfs. Spectroscopic observations of molecules and atoms in planetary atmospheres are also important, whereas current telescopes cannot directly image the planet due to its proximity to the central star. In the future, it will be one of the targets of life searches by 30-meter range telescopes.

So far, only three planets have been known to have such an orbit. low mass stars, including Proxima Centauri b. IRD-SSP is expected to continue the search for new planets.

“Ross 508b is the first successful detection of a super-Earth using only near-infrared spectroscopy. Previously, in the detection of low-mass planets such as super-Earths, near-infrared observations alone were not accurate enough, and the verification view High-precision line-of-sight velocity measurements were required in light.This study shows that IRD-SSP alone is capable of detecting planetsAnd clearly demonstrates the advantage of IRD-SSP in its ability to search with high precision, even for late typists. red dwarf who are too faint to see visible light“The discovery paper’s lead author Dr. Hiroki Harakawa (NAOJ Subaru Telescope) says.

“It has been 14 years since the start of the development of the IRD. We have continued our development and research with the hope of finding a planet like Ross 508 b. This discovery was made possible due to the IRD’s high instrumental performance, large aperture Subaru The telescope, and the strategic framework of observations that enables in-depth and consistent data acquisition. We are committed to making new discoveries.” Professor Bunei Sato (Tokyo Institute of Technology), IRD-SSP’s principal investigator, says.

These results emerged as those of Harakawa et al. “A Super-Earth orbiting near the inner edge of the habitable zone around M4.5-dwarf Ross 508” Publications of the Astronomical Society of Japan on 30 June 2022.


Super-Earth exoplanet discovered nearby star


more information:
Hiroki Harakawa et al, a super-Earth M4.5 dwarf orbiting near the inner edge of the habitable zone around Ross 508, Publications of the Astronomical Society of Japan (2022). DOI: 10.1093/pasj/psac044

Citation: Super-Earth Ross 508b Skim Habitable Zone of Red Dwarfs (2022, Aug 1) from https://phys.org/news/2022-08-super-earth-ross-508b-skims-habitable.html on 2 Aug 2022 have gotten

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