Transiting Exoplanet Survey Satellite

TESS was launched on April 18, 2018, aboard a SpaceX Falcon 9 rocket from Cape Canaveral. Its unique 13.7-day highly elliptical orbit, with a perigee of about 108,000 km and apogee of about 373,000 km, allows the spacecraft to remain in a stable resonance with the Moon, minimizing orbital perturbations. The orbit is also designed to keep the satellite away from Earth's radiation belts and to provide continuous viewing of the southern and northern ecliptic hemispheres. TESS uses four wide-field CCD cameras, each with a 24° × 24° field of view, covering a combined 2300 square degrees per observation. The satellite operates in a 2:1 lunar resonance, which ensures that its orbital period is exactly half of the Moon's sidereal period, providing long-term stability without the need for frequent station-keeping maneuvers.

TESS divides the sky into 26 sectors, each observed for about 27 days, with the southern hemisphere covered in the first year and the northern hemisphere in the second year. The mission's primary goal is to find small planets around bright stars, enabling detailed characterization of their masses, densities, and atmospheric compositions. TESS has discovered a wide range of planets, including hot Jupiters, super-Earths, and rocky worlds in the habitable zones of their stars. Notable finds include TOI-700 d, an Earth-sized planet in the habitable zone of its star, and the TESS Objects of Interest (TOIs) catalog, which has grown to over 7,000 candidates. TESS also monitors variable stars, supernovae, and other transient phenomena, contributing to time-domain astronomy. The mission's data are released publicly through the Mikulski Archive for Space Telescopes (MAST), enabling a global community of researchers to mine the data for new discoveries.

TESS has become a cornerstone of exoplanet science, providing targets for ground-based observatories and space telescopes like the James Webb Space Telescope (JWST). Its discoveries have enabled detailed atmospheric studies, such as the detection of carbon dioxide in the atmosphere of a hot gas giant. TESS has also identified exoplanets around stars that are bright enough for radial velocity measurements, leading to precise mass determinations. The mission has been extended beyond its primary two-year survey, with additional years of observations focusing on the ecliptic poles and revisiting sectors to detect longer-period planets. TESS's legacy includes not only thousands of planets but also a deeper understanding of stellar variability, binary systems, and the demographics of planetary systems. The satellite is expected to continue operating until at least 2025, with the possibility of further extensions.

Beyond exoplanets, TESS has contributed to the study of comets, asteroids, and even the search for exomoons. The satellite's full-frame images have been used to detect stellar flares and to study the rotation of stars. TESS also observed the aftermath of a tidal disruption event, where a star was shredded by a supermassive black hole. The mission's data have been used to discover a new class of pulsating white dwarfs and to measure the ages of stellar clusters. TESS has also been used to observe the gravitational lensing of a background star by a foreground object, providing a rare test of general relativity. The satellite's cameras have captured the passage of interstellar comet 2I/Borisov, and its data have been used to study the variability of active galactic nuclei. TESS's unique orbit and wide field of view make it a versatile tool for a wide range of astrophysical research, far beyond its original exoplanet-focused mission.

Transit

The passage of a planet in front of its host star, causing a periodic dip in the star's brightness.

Exoplanet

A planet that orbits a star outside our solar system.

Habitable zone

The region around a star where liquid water could exist on a rocky planet's surface.

TOI

TESS Object of Interest; a star that shows a transit-like signal in TESS data, potentially indicating a planet.