Saturday, October 1, 2022

Astronomers have found a super-Earth near its star’s habitable zone

The very small motion of a small star has revealed the presence of a super-Earth exoplanet, orbiting at a habitable distance.

Around a faint red dwarf called Ross 508, which lies only 36.5 light-years away (yet too dim to be seen with the naked eye), astronomers have confirmed the existence of a world just 4 times the mass of Earth. Given what we know about the mass range of planets, this means that the worlds are likely to be terrestrial, or rocky, rather than gaseous.

As we know, the exoplanet named Ross 508 b is unlikely to be habitable for life; However, the discovery, for the first time, for a new survey using the National Astronomical Observatory of Japan (NAOJ) Subaru Telescope in Hawaii, demonstrates the efficacy of techniques used to detect minor planets around dim stars.

The search for habitable exoplanets is somewhat hindered by the nature of what we consider those exoplanets to be like. The only template we have is Earth: a relatively small planet, orbiting at a distance from its star where the temperature is favorable to that of liquid water on the surface. This is known as the ‘habitable zone’.

For example, they’re not the only factors, obviously — Mars falls inside the Sun’s habitable zone — but they’re the easiest to screen.

However, the techniques we use to search for exoplanets work best on large worlds, such as gas giants, orbiting at very close distances, too hot for liquid water. That doesn’t mean we can’t find other kinds of worlds, but it’s more difficult.

The main technique for finding exoplanets is the transit method. NASA’s exoplanet-hunting telescope uses TESS and its first Kepler. An instrument stares at the stars, searching for regular dips in their light caused by an object orbiting regularly between us and the star.

The depth of this transit can be used to calculate the mass of the object; The bigger the light curve – due to the larger planets – the easier it is.

At the time of writing, 3,858 exoplanets have been confirmed using this method.

The second most useful technique is the radial velocity method, also known as the Wobble or Doppler method. When two bodies are locked in orbit, one does not orbit the other; Rather, they orbit a mutual center of gravity. This means that the gravitational effect of any of the orbiting planets tends to slightly move a star in that spot – yes, even the Sun.

Thus, the star-light star reaching Earth is very dimly Doppler shifted. As it moves towards us, the light is compressed slightly to a bluer wavelength, and as it is moving away, it is pulled into a redder wavelength. This technique is better at detecting smaller exoplanets with wider orbits.

In 2019, an international team of astronomers led by NAOJ began a survey using the Subaru Telescope to search for dim red dwarf stars for exoplanets by identifying Doppler shifts in infrared and near-infrared wavelengths. This allows the discovery of fainter, and therefore older and more established, red dwarf stars.

Ross 508 b, described in a paper led by Subaru Telescope astronomer Hiroki Harakawa, is the expedition’s first exoplanet, and it is a promising one. The world is about 4 times the mass of the Sun, orbiting the star every 10.75 days.

It is very close to Earth’s orbit, you may have noticed; But Ross 508 is much smaller and lighter than the Sun. At that distance, the stellar radiation hitting Ross 508 b is just 1.4 times the solar radiation hitting Earth. This places the exoplanet very close to the outer inner edge of its star’s habitable zone.

This discovery bodes very well for the future. For one, Ross 508 b transits its star. This means that TESS, which was turned over to the star field of the sky in April and May of this year, will have acquired enough transit data for astronomers to determine whether the exoplanet has an atmosphere. Such observations could help scientists characterize world environments that may be more habitable.

In addition, Ross 508, at 18 percent the mass of the Sun, is one of the smallest, weakest stars with an orbiting world discovered using radial velocity. This suggests that future radial velocity surveys at infrared wavelengths have the potential to uncover a vast ensemble of exoplanets orbiting dim stars and reveal the diversity of their planetary systems.

The team’s research has been accepted in Publications of the Astronomical Society of Japanand is available on arXiv.

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Nation World News Desk
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