Context

• NASA’s planet-hunting probe Transiting Exoplanet Survey Satellite (TESS), has discovered a new exoplanet named HD 21749b outside our solar system.
• This is the third new planet confirmed by the TESS since its launch in April 2018. The other two being Pi Mensae b and the LHS 3844b.

About

Main findings

• The exoplanet orbits a bright, nearby dwarf star about 53 light years away, in the constellation
• HD 21749b orbits around its star in 36 days, compared to the two other planets — Pi Mensae b, a “super-Earth” with a 6.3-day orbit, and LHS 3844b, a rocky world that speeds around its star in just 11 hours.
• It’s the coolest small planet that has been discovered so far which revolves around a star outside of our own solar system.
• The planet is about three times the size of the earth, which puts it in the category of a “sub-Neptune.”

What is Transiting Exoplanet Survey Satellite Mission (TESS)?

• TESS is a NASA-sponsored Astrophysics Explorer-class mission that is performing a 2-year all-sky survey to search for planets transiting nearby stars.
• It will discover planets smaller than Neptune that transit stars bright enough to enable follow-up spectroscopic observations that can provide planet masses and atmospheric compositions
• It will monitor about 200,000 main-sequence dwarf stars to detect periodic drops in brightness caused by planetary transits.

Is it the first mission to explore the exoplanets?

• No, earlier NASA's Kepler Mission conducted a statistical transit survey designed to determine the frequency of Earth-sized planets around other stars.
• Kepler revealed thousands of exoplanets orbiting stars in its 115 square degree field-of view, which covered about 0.25 percent of the sky.
• While Kepler was revolutionary in its finding that Earth-to-Neptune-sized planets are common, the bulk of the stars in the Kepler field lie at distances of hundreds to thousands of parsecs, making it difficult to obtain ground-based follow-up observations for many systems.

What is speciality of TESS over Kepler Mission?

• The TESS Mission is designed to survey over 85% of the sky (an area of sky 400 times larger than covered by Kepler) to search for planets around nearby stars (within ~200 parsec).
• TESS stars will typically be 30-100 times brighter than those surveyed by the Kepler satellite.
• Planets detected around these stars will therefore be far easier to characterize with follow-up observations, resulting in refined measurements of planet masses, sizes, densities, and atmospheric properties.