First tidally locked super-Earth exoplanet confirmed

News Excerpt:

An international team of astronomers and astrophysicists has confirmed the first known observance of a tidally locked super-Earth exoplanet.

More about the news:

  • Scientists have confirmed the existence of a super-Earth exoplanet, named LHS 3844b, that is tidally locked to its star. 
  • This means that one side of the planet is always facing its star, while the other side is perpetually turned away.
  • The team’s innovative approach to studying the planet’s characteristics has shed light on a phenomenon that, while suspected in exoplanets, had not been conclusively proven until now.

What is a Super-Earth?

  • Super-Earths – a class of planets unlike any in our solar system – are more massive than Earth yet lighter than ice giants like Neptune and Uranus and can be made of gas, rock, or a combination of both.
  • They are between twice the size of Earth and up to 10 times its mass.

What is an Exoplanet?

  • An exoplanet is any planet beyond our solar system.
  • Most exoplanets orbit other stars, but free-floating exoplanets, called rogue planets, orbit the galactic center and are untethered to any star. 

Tidal Locking:

  • Tidal locking happens when an object’s orbital period matches its rotation period, leading to the same side always facing the planet or star it orbits. 
  • Tidal locking is a natural consequence of the gravitational distortions induced by a body on another.
  • The Moon is tidally locked to the Earth because it rotates in exactly the same time as it takes to orbit the Earth. That is why we only see one side of the Moon.
    • For this reason, the Moon has what is commonly described as a "far side"—the side we never see.

Methodology of the study:

  • To determine if LHS 3844b was indeed tidally locked, the research team used the data from the Spitzer Space Telescope. 
  • Researchers used infrared data from the Spitzer Space Telescope to assess the level of starlight reflection from the exoplanet LHS 3844b, a super-Earth.
  • Infrared reflections allowed the team to calculate the temperature of the planet's surface. 
  • By doing so at different points in the orbit of its star, the team was able to determine that one side of the planet was much cooler than the other—a difference great enough to show that the cool side never faced the star.

LHS 3844b:

  • LHS 3844b is a super Earth exoplanet that orbits an M-type star.
  • Its mass is 2.25 times that of Earth, it takes 0.5 days to complete one orbit of its star, and is 0.00622 AU from its star.
  • Its discovery was announced in 2019. 

Significance of the discovery:

  • Finding one tidally locked planet strongly suggests that there are many more of them and many of the planets in the Milky Way galaxy are likely tidally locked.
  • Some of the tidally locked planets may be able to harbour life along the boundary between hot and cold.

Spitzer Space Telescope:

  • Spitzer was the final mission launched in NASA's Great Observatories Program – a family of four space-based observatories, each studying the universe in a different kind of light. 
  • To complement the visible-light Hubble Space Telescope, the Compton Gamma-Ray Observatory, and the Chandra X-Ray Observatory, Spitzer was designed to detect infrared radiation, which is primarily heat radiation, allowing us to peer into regions of space hidden from optical telescopes.

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