HD 85512 b is an

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

orbiting HD 85512, a

K-type main-sequence star A K-type main-sequence star, also referred to as a K-type dwarf or an orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ...

approximately 37

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s from Earth in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellation ...

of Vela. Due to its mass of at least 3.6 times the mass of Earth, HD 85512 b is classified as a rocky Earth-size exoplanet (< 5M_🜨) and is one of the smallest exoplanets discovered to be just outside the inner edge of the

habitable zone In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kas ...

. HD 85512 b, along with

Gliese 581 d Gliese 581d (often shortened to Gl 581d or GJ 581d) is a proposed extrasolar planet orbiting within the Gliese 581 system, approximately 20.4 light-years away in the Libra constellation. It is the third planet claimed in the system and (assum ...

, was once considered to be one of the best candidates for habitability in 2011.

Physical characteristics

Mass, radius and temperature

The planet has a ''minimum'' Earth mass of 3.6 ± 0.5, ''minimum''

surface gravity The surface gravity, ''g'', of an astronomical object is the gravitational acceleration experienced at its surface at the equator, including the effects of rotation. The surface gravity may be thought of as the acceleration due to gravity experien ...

of about 1.4 g and assuming an atmosphere like Earth's despite its far greater mass, an estimated temperature of 298 K (24.85 °C or 76.73 °F) at the top of its atmosphere. The estimated temperature is noted to be similar to temperatures in

Southern France Southern France, also known as the South of France or colloquially in French as , is a defined geographical area consisting of the regions of France that border the Atlantic Ocean south of the Marais Poitevin,Louis Papy, ''Le midi atlantique'', A ...

, but various atmospheric conditions prevalent in the planet have to be analyzed to estimate the temperature of the surface. An estimated radius of 1.3 is possible based on its mass.

Host star

The planet orbits a ( K-type)

star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth ma ...

named HD 85512. The star has a mass of 0.69 and a radius of around 0.53 . It has a surface temperature of 4715 K and is 5.61 billion years old. In comparison, the Sun is about 4.6 billion years old and has a surface temperature of 5778 K. The star's

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...

, or how bright it appears from Earth's perspective, is 7.43 Therefore, HD 85512 is too dim to be seen with the naked eye, but can be viewed using good binoculars.

Orbit

The planet orbits the parent star (which has about 11% of the Sun's luminosity) at a distance of about 0.26 AU, with an orbital period of about 54 days, and is possibly tidally locked.

Habitability and climate

Models generated by ''Pepe et al (2011)'' suggest that for the temperature to be below 270 K (-3.15 °C), for a circular orbit, the planetary

albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...

should be 0.48 ± 0.05 and for an eccentricity of 0.11, the planetary albedo should be 0.52. If the planet has 50% cloud cover, water may exist in liquid form on the planet provided its atmosphere is similar to our own, thus increasing the planet's habitability potential. Also, if the albedo of the planet is increased due to cloud cover, water could be present in its liquid form on the planet, which would mean that the planet is on the edge of the habitability zone. However, PHL's new definition of the circumstellar habitable zone classifies this planet in the "too hot" zone, and it considers the planet "not habitable". The planet would likely be inhospitable because of a

runaway greenhouse effect A runaway greenhouse effect occurs when a planet's atmosphere contains greenhouse gas in an amount sufficient to block thermal radiation from leaving the planet, preventing the planet from cooling and from having liquid water on its surface. A ...

on its surface. Any oceans on its surface would have boiled away due to the high stellar flux, and as this occurred, the temperature would have risen to around . The

water vapor (99.9839 °C) , - , Boiling point , , - , specific gas constant , 461.5 J/( kg·K) , - , Heat of vaporization , 2.27 MJ/kg , - , Heat capacity , 1.864 kJ/(kg·K) Water vapor, water vapour or aqueous vapor is the gaseous phas ...

would have accumulated in the atmosphere to the point where the surface temperature would rise to around as the planet would have been overwhelmed by water vapor—a powerful greenhouse gas.http://csep10.phys.utk.edu/astr161/lect/venus/greenhouse.html Little amounts of carbon dioxide would have been present, as HD 85512 b was probably an

ocean planet An ocean world, ocean planet, panthalassic planet, maritime world, water world or aquaplanet, is a type of planet that contains a substantial amount of water in form of oceans, either beneath the surface, as subsurface oceans, or on the sur ...

(with little to no landmasses) very shortly after its star was formed into the

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar H ...

, before the stellar flux increased to its estimated present state. The surface pressure would have also increased to about 100 times Earth's surface pressure (100

kilopascal The pascal (symbol: Pa) is the unit of pressure in the International System of Units (SI), and is also used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength. The unit, named after Blaise Pascal, is define ...

s, 100 atm) because of the amount of water vapor in the atmosphere. Thus, HD 85512 b is likely a

desert planet A desert planet, also known as a dry planet, an arid planet, or a dune planet, is a theoretical type of terrestrial planet with a surface consistency similar to Earth's hot deserts. History A 2011 study suggested that not only are life-sustain ...

rather than an ocean planet because of the increased stellar flux.

Discovery

HD 85512 b was discovered by scientists at

University of Geneva The University of Geneva (French: ''Université de Genève'') is a public research university located in Geneva, Switzerland. It was founded in 1559 by John Calvin as a theological seminary. It remained focused on theology until the 17th centur ...

, Switzerland, led by Swiss astronomer

Stéphane Udry Stéphane Udry (born 1961 in Sion, Switzerland) is an astronomer at the Geneva Observatory in Switzerland, whose current work is primarily the search for extra-solar planets. He and his team, in 2007, discovered a possibly terrestrial planet in ...

of the Guaranteed Time Observations (GTO) program of High Accuracy Radial velocity Planet Searcher (

HARPS The High Accuracy Radial Velocity Planet Searcher (HARPS) is a high-precision echelle planet-finding spectrograph installed in 2002 on the ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003. ...

), a high-precision echelle

spectrograph An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify mat ...

installed on

ESO The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental research organisation made up of 16 member states for ground-based ast ...

's 3.6 m telescope at

La Silla Observatory La Silla Observatory is an astronomical observatory in Chile with three telescopes built and operated by the European Southern Observatory (ESO). Several other telescopes are located at the site and are partly maintained by ESO. The observatory i ...

in Chile. The team used the

Doppler spectroscopy Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in t ...

technique which determines the

minimum mass In astronomy, minimum mass is the lower-bound calculated mass of observed objects such as planets, stars and binary systems, nebulae, and black holes. Minimum mass is a widely cited statistic for extrasolar planets detected by the radial veloc ...

of the planet through slight changes in motion of the parent star. It was discovered on August 17, 2011. On August 17, 2011, researchers released a study of the planet. The study makes assumptions about the planet actually having the minimum mass allowed by existing observations, not being tidally locked, and having one specific composition out of the wide parameter set available to conclude that HD 85512 b is the most habitable exoplanet discovered up to that point and one of the most stable exoplanets discovered by the High Accuracy Radial Velocity Planet Searcher.

Possibility as target for interstellar probe

Reaching this planet at the current record spacecraft speed, the Helios Probes' , would take 156,971 years.

References

External links

A Habitable Planet around HD 85512
{{Sky, 09, 51, 07.1, -, 43, 30, 10, 36.3 HD 85512 Exoplanets discovered in 2011 Exoplanets detected by radial velocity Near-Earth-sized exoplanets Vela (constellation)