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Explained: How A Wobble Revealed A New World Just 36 Light-Years From Us

Astronomers have discovered a “super-Earth” planet orbiting the star GJ 740, a red dwarf star about 36 light years from the Earth.

A “super-Earth” planet sounds like an exciting place, right? Bigger than our own planet, but otherwise Earth-like, is what most people presume it means.

Not quite.

What is a ‘super-Earth?’

It’s a loose, rather misleading term for a kind of planet that doesn’t exist in our own Solar System. That in itself is puzzling, because we find super-Earths in a very many star systems.

At least twice as massive than Earth and as big as 10 times as massive, super-Earths are lighter than ice giant planets (like Neptune and Uranus). They can be made of gas and/or rock.

What is a ‘red dwarf’ star?

By far the most common type of star in our region of the Milky Way, red dwarf stars are cooler, smaller and less massive than our Sun. Officially they have effective surface temperatures between 2,400-3,700 K—way cooler than the Sun—and are anywhere between 0.08 and 0.45 its mass.

GJ 740, which is 36 light-years in the Serpens constellation in the night sky, is such a star.

What we know about GJ 740 b

Here’s what we know about GJ 740 b, as published in Astronomy & Astrophysics by a team of researchers at the Instituto de Astrofísica de Canarias (IAC) in the Canary Islands, Spain.

  • Its mass is 2.96 Earths.
  • It’s probably a rocky planet.
  • It takes 2.4 days to complete one orbit of its star.
  • It orbits 0.029 AU from its star—a tiny fraction of the distance between the Earth and the Sun.

The importance of GJ 740 b

“This is the planet with the second shortest orbital period around this type of star,” said first author Borja Toledo Padrón, a Severo Ochoa-La Caixa doctoral student. “The mass and the period suggest a rocky planet, with a radius of around 1.4 Earth radii.” He thinks it could be a prime target for very large telescopes planned for “first light” the end of the 2020s, such as:

The team’s data also indicates the presence of a second planet with an orbital period of nine years. It appears to be about the same mass as planet Saturn—about 100 times the mass of Earth—but it’s not a confirmed detection.

How GJ 740 b was found

While many exoplanets are found when they transit their star and caused their light to dip, that restricts astronomers to only discovering them around star systems aligned with our own. GJ 740 b was found using the radial velocity method; a very slight “wobble” of a star caused by the gravitational attraction of a planet in orbit around it.

Wishing you clear skies and wide eyes.