Gliese 581e

{{Short description|Terrestrial planet orbiting Gliese 581}}

{{Infobox planet

| name = Gliese 581e

| image = Exoplanet Comparison Gliese 581 e.png

| caption = Size comparison of Gliese 581e with Earth
(Based on selected hypothetical modeled compositions){{efn|The estimated range of sizes in this image from 2009 is based on the planet's minimum mass. Since the true mass is now known to be somewhat greater, the sizes may be underestimated.}}

| discovery_ref =

| discoverer = Mayor et al.

| discovery_site = La Silla Observatory, Chile

| discovered = 21 April 2009

| discovery_method = Radial velocity

| orbit_ref =

| apsis = astron

| semimajor = {{val|0.02799|0.0003|ul=AU}}

| eccentricity = {{val|0.012|0.015|0.008}}

| period = {{val|3.1481|0.0004|ul=d}}

| inclination = {{val|47|15|13|u=deg}}

| time_periastron = 2454752.33 ± 0.05

| arg_peri = {{val|226|91|55|u=deg}}

| semi-amplitude = {{val|1.8|0.1|ul=m/s}}

| star = Gliese 581

| physical_ref =

| mass = {{val|2.48|0.70|0.42|ul=Earth mass}}

}}

Gliese 581e {{IPAc-en|ˈ|ɡ|l|iː|z|ə}} or Gl 581e is an exoplanet orbiting within the Gliese 581 system, located {{convert|20.5|ly|pc|lk=on|abbr=off}} away from Earth in the Libra constellation. It is the third planet discovered in the system (fourth if the disputed planet candidate Gliese 581d is included) and the first in order from the star.

The planet was discovered by an Observatory of Geneva team led by Michel Mayor, using the HARPS instrument on the European Southern Observatory {{convert|3.6|m|in|abbr=on}} telescope in La Silla, Chile. The discovery was announced on 21 April 2009. Mayor's team employed the radial velocity technique, in which the orbit size and mass of a planet are determined based on the small perturbations it induces in its parent star's orbit via gravity.

With a minimum mass of about 1.9 Earth masses, Gliese 581e was the least massive exoplanet known around a normal star at the time of discovery in 2009, with only PSR B1257+12 A being less massive.{{cite web|last=Rincon|first=Paul|author2=Amos, Jonathan|url=http://news.bbc.co.uk/1/hi/sci/tech/8008683.stm|title=Lightest exoplanet is discovered|publisher=BBC|date=2009-04-21|access-date=2009-04-21|archive-date=2009-04-24|archive-url=https://web.archive.org/web/20090424061149/http://news.bbc.co.uk/1/hi/sci/tech/8008683.stm|url-status=live}}{{cite news |first=Dennis |last=Overbye |title=Astronomers Find Planet Closer to Size of Earth |url=https://www.nytimes.com/2009/04/22/science/22planet.html |work=New York Times |date=April 21, 2009 |access-date=February 24, 2017 |archive-date=March 12, 2017 |archive-url=https://web.archive.org/web/20170312213033/http://www.nytimes.com/2009/04/22/science/22planet.html |url-status=live }} A 2024 study determined the orbital inclination of the planet, allowing its true mass to be determined, which is about 30% greater than the minimum mass at about 2.5 Earth masses.

Gliese 581e completes an orbit around its parent star in 3.15 days. At an orbital distance of just {{convert|0.028|AU|km|abbr=on|lk=in}} from its parent star, it orbits further in than the habitable zone. Although scientists think it probably has a rocky surface similar to Earth, it is also likely to experience intense tidal heating similar to (and likely more intense than) that affecting Jupiter's moon Io.{{cite journal| last1 = Barnes | first1 = Rory| last2 = Jackson | first2 = Brian| last3 = Greenberg | first3 = Richard| last4 = Raymond | first4 = Sean N. |title=Tidal Limits to Planetary Habitability|date=2009-06-09| doi = 10.1088/0004-637X/700/1/L30| journal = The Astrophysical Journal| volume = 700| issue = 1| pages = L30–L33|arxiv=0906.1785|bibcode = 2009ApJ...700L..30B | s2cid = 16695095}}