Mega-Earth

{{short description|Terrestrial planet with ten times the mass of Earth}}

File:Exoplanet Comparison Kepler-10 c.png, with Earth and Neptune]]

A mega-Earth is a proposed neologism for a massive terrestrial exoplanet that is at least ten times the mass of Earth. Mega-Earths would be substantially more massive than super-Earths (terrestrial and ocean planets with masses around 5–10 Earths). The term "mega-Earth" was coined in 2014, when Kepler-10c was revealed to be a Neptune-mass planet with a density considerably greater than that of Earth,{{cite web|url=https://www.cfa.harvard.edu/news/2014-14|title=Astronomers Find a New Type of Planet: The "Mega-Earth"2014-14|archive-url=https://web.archive.org/web/20140602204141/https://www.cfa.harvard.edu/news/2014-14|archive-date=2 June 2014}} though it has since been determined to be a typical volatile-rich planet weighing just under half that mass.

Examples

Kepler-10c was the first exoplanet to be classified as a mega-Earth. At the time of its discovery, it was believed to have a mass around 17 times that of Earth ({{Earth mass|link=yes}}) and a radius around 2.3 times Earth's ({{Earth radius|link=yes}}), giving it a high density that implied a mainly rocky composition. However, several follow-up radial velocity studies produced different results for Kepler-10c's mass, all much below the original {{Earth mass|17}} estimate. In 2017, a more careful analysis using data from multiple different telescopes and spectrographs found that Kepler-10c is more likely around {{Earth mass|7.4}}, making it a typical volatile-rich mini-Neptune and not a mega-Earth.{{cite journal | arxiv=1707.06192 | doi=10.1093/mnrasl/slx116 | doi-access=free | title=Pinning down the mass of Kepler-10c: The importance of sampling and model comparison | date=2017 | last1=Rajpaul | first1=V. | last2=Buchhave | first2=L. A. | last3=Aigrain | first3=S. | journal=Monthly Notices of the Royal Astronomical Society: Letters | volume=471 | pages=L125–L130 }}[https://astrobites.org/2017/08/07/the-mass-of-kepler-10c-revisited-upping-the-radial-velocities-game/ The mass of Kepler-10c revisited: upping the radial velocities game], Leonardo dos Santos, 7 August 2017, Astrobites

K2-56b, also designated BD+20594b, is a much more likely mega-Earth,{{cite conference |url=https://www.hou.usra.edu/meetings/lpsc2017/pdf/1078.pdf |title=BD+20594B: A Mega-Earth Detected in the C4 field of the Kepler K2 mission |first=P |last=Futó |year=2017 |conference=48th Lunar and Planetary Science Conference |conference-url=https://www.hou.usra.edu/meetings/lpsc2017/ |language=en |access-date=6 September 2020}} with about {{Earth mass|16}} and {{Earth radius|2.2}}. At the time of its discovery in 2016, it had the highest chance of being rocky for a planet its size, with a posterior probability that it is dense enough to be terrestrial at about 0.43. For comparison, at the time the corresponding probability for Kepler-10c was calculated as 0.1, and as 0.002 for Kepler-131b.{{cite journal | arxiv=1601.07608 | doi=10.3847/0004-637X/830/1/43 | doi-access=free | title=Discovery and Validation of a High-Density Sub-Neptune from the K2 Mission | date=2016 | last1=Espinoza | first1=Néstor | last2=Brahm | first2=Rafael | last3=Jordán | first3=Andrés | last4=Jenkins | first4=James S. | last5=Rojas | first5=Felipe | last6=Jofré | first6=Paula | last7=Mädler | first7=Thomas | last8=Rabus | first8=Markus | last9=Chanamé | first9=Julio | last10=Pantoja | first10=Blake | last11=Soto | first11=Maritza G. | last12=Morzinski | first12=Katie M. | last13=Males | first13=Jared R. | last14=Ward-Duong | first14=Kimberly | last15=Close | first15=Laird M. | journal=The Astrophysical Journal | volume=830 | issue=1 | page=43 | bibcode=2016ApJ...830...43E }}

Kepler-145b is one of the most massive planets classified as mega-Earths, with a mass of {{Earth mass|37.1}} and a radius of {{Earth radius|2.65}}, so large that it could belong to a sub-category of mega-Earths known as supermassive terrestrial planets (SMTP). It likely has an Earth-like composition of rock and iron without any volatiles. A similar mega-Earth, K2-66b, has a mass of about {{Earth mass|21.3}} and a radius of about {{Earth radius|2.49}}, and orbits a subgiant star. Its composition appears to be mainly rock with a small iron core and a relatively thin steam atmosphere.{{cite conference |url=https://www.hou.usra.edu/meetings/lpsc2018/pdf/1224.pdf |title=Kepler-145b and K2-66b: A Kepler- and a K2-Mega-Earth with Different Compositional Characteristics |first=P |last=Futó |year=2018 |conference=49th Lunar and Planetary Science Conference |conference-url=https://www.hou.usra.edu/meetings/lpsc2018/ |language=en |access-date=6 September 2020}}

Kepler-277b and Kepler-277c are a pair of planets orbiting the same star, both thought to be mega-Earths with masses of about {{Earth mass|87.4}} and {{Earth mass|64.2}}, and radii of about {{Earth radius|2.92}} and {{Earth radius|3.36}}, respectively.{{cite conference |url=http://www.hou.usra.edu/meetings/lpsc2020/pdf/1055.pdf |title=Kepler-277 b: A Supermassive Terrestrial Exoplanet in the Kepler-277 Planetary System |first=P |last=Futó |year=2020 |conference=51st Lunar and Planetary Science Conference |conference-url=https://www.hou.usra.edu/meetings/lpsc2020/ |language=en |access-date=6 September 2020}}

PSR J1719−1438 b is the most massive mega-Earth ever known with a mass of about {{Earth mass|330}} and a radius less than {{Earth radius|4}}. PSR J1719−1438 b is a pulsar planet which is most likely composed largely of crystalline carbon but with a density far greater than diamond.{{cite news |last=Hirschler |first=Ben |date=August 25, 2011 |title=Astronomers discover planet made of diamond |work=Reuters |url=https://www.reuters.com/article/us-planet-diamond-idUSTRE77O69A20110825 |access-date=August 25, 2011}}{{cite journal |last1=Bailes |first1=M. |last2=Bates |first2=S. D. |last3=Bhalerao |first3=V. |last4=Bhat |first4=N. D. R. |last5=Burgay |first5=M. |last6=Burke-Spolaor |first6=S. |last7=d'Amico |first7=N. |last8=Johnston |first8=S. |last9=Keith |first9=M. J. |last10=Kramer |first10=M. |last11=Kulkarni |first11=S. R. |display-authors=2 |date=August 25, 2011 |title=Transformation of a Star into a Planet in a Millisecond Pulsar Binary |url=https://www.science.org/doi/10.1126/science.1208890 |journal=Science |volume=333 |issue=6050 |pages=1717–1720 |arxiv=1108.5201 |bibcode=2011Sci...333.1717B |doi=10.1126/science.1208890 |pmid=21868629 |last12=Levin |first12=L. |last13=Lyne |first13=A. G. |last14=Milia |first14=S. |last15=Possenti |first15=A. |last16=Spitler |first16=L. |last17=Stappers |first17=B. |last18=Van Straten |first18=W. |s2cid=206535504}}

References

=Works cited=

{{cite conference |url=https://www.hou.usra.edu/meetings/lpsc2018/pdf/1453.pdf |title=Basic Mineralogical Models for Silicate- and Carbon-Rich Mega-Earths Considering Compositional and Geophysical Constraints |first1=P |last1=Futó |first2=A |last2=Gucsik |year=2018 |conference=49th Lunar and Planetary Science Conference |conference-url=https://www.hou.usra.edu/meetings/lpsc2018/ |language=en |access-date=6 September 2020}}{{rs?|date=July 2021}}

Mega-Earth

Examples

See also

References

=Works cited=

Further reading