Scientists Discover Mega-Earth GJ 523b

GJ 523b is an exoplanet identified as a “mega-Earth” with a radius about 2.55 times that of Earth and a mass of 23.5 Earth masses. It orbits a mid-K dwarf star and has an estimated bulk density of about 7.8 grams per cubic centimetre.

Exoplanet Classification

Exoplanets are planets that orbit stars outside the Solar System. A “mega-Earth” is a proposed class of rocky exoplanet with a radius of at least 2.1 Earth radii and a density of at least 5.5 grams per cubic centimetre.

Physical and Orbital Features

GJ 523b completes one orbit around its host star in 17.75 days. Its estimated zero-albedo equilibrium temperature is 538 Kelvin, and its minimum orbital obliquity is 71.4 degrees, which places it in a highly tilted polar orbit.

Observation Methods and Instruments

The planet’s properties were derived from transit data and radial velocity measurements. NASA’s Transiting Exoplanet Survey Satellite (TESS) provided transit observations, while the NEID spectrograph on the WIYN 3.5-metre Telescope in Arizona supplied radial velocity data.

Important Facts for Exams

• Exoplanets are also called extrasolar planets because they orbit stars beyond the Solar System.
• Transit photometry measures the dip in starlight when a planet passes in front of its host star.
• Radial velocity measurements detect the wobble of a star caused by an orbiting planet’s gravity.
• Bulk density is calculated from mass and volume and is used to infer rocky, icy, or gaseous composition.

Scientific Context

GJ 523b is part of a planetary system estimated to be 169 million years old. A rocky core of 23.5 Earth masses would normally be expected to accrete a thick gas envelope and form a gas giant.