Kepler-37b
{{Short description|Sub-Earth orbiting Kepler-37, currently the smallest known exoplanet}}
{{Infobox planet
| name = Kepler-37b
| image = Kepler-37b.jpg
| caption = Artist's impression of Kepler-37b.
| discovery_site = Kepler space telescope
| discovered = February 20, 2013
| discovery_method = Transit
| apsis = astron
| semimajor = {{val|0.1019|0.0014|ul=AU}}
| eccentricity = <0.098
| period = {{val|13.367020|(60)|ul=d}}
| inclination = {{val|88.63|0.30|0.53|u=deg}}
| star = Kepler-37
| mean_radius = {{val|0.3098|0.0059|0.0076|ul=Earth radius}}
| mass = {{val|p=<|0.79|ul=Earth mass}}Masses more than a few times that of the Moon result in unphysically high densities.
| single_temperature = {{val|718|10|ul=K}} ({{convert|718|K|C F|disp=out}}, equilibrium)
}}
Kepler-37b is an exoplanet orbiting the star Kepler-37 in the constellation Lyra. {{As of|2013|02}}, it is the smallest planet discovered around a main-sequence star, with a radius slightly greater than that of the Moon and slightly smaller than that of Mercury. The measurements do not constrain its mass, but masses above a few times that of the Moon give unphysically high densities.
Characteristics
=Mass, radius and temperature=
{{Planetary radius
| align =
| base = Earth
| Exoplanet = Kepler-37b
| radius = 31
}}
Kepler-37b is a sub-Earth, an exoplanet with a radius and mass smaller than Earth. Its equilibrium temperature is {{convert|718|K|C F}}. Because of its small size and high temperatures, it is not expected to have an atmosphere. Its radius is approximately 0.31 {{Earth radius}} (about {{convert|1980|km|mi}}), slightly larger than the Moon (0.27 {{Earth radius}}), but a little smaller than Mercury (0.38 {{Earth radius}}). Due to its small size, it is very likely Kepler-37b is a rocky planet with a solid surface. Furthermore, it is too hot to support liquid water on its surface.
=Host star=
{{main|Kepler-37}}
The planet orbits a (G-type) star similar to the Sun, named Kepler-37, orbited by a total of four planets. The star has a mass of 0.80 {{solar mass}} and a radius of 0.79 {{solar radius}}. It has a temperature of, 5417 K and is 5.66 billion years old. In comparison, the Sun is 4.6 billion years old,{{cite web |url=http://www.universetoday.com/18237/how-old-is-the-sun/ |title=How Old is the Sun? |author=Fraser Cain |date=16 September 2008|publisher=Universe Today |access-date=19 February 2011}} and has a temperature of 5778 K.{{cite web |url=http://www.universetoday.com/18092/temperature-of-the-sun/ |title=Temperature of the Sun |author=Fraser Cain |date=15 September 2008|publisher=Universe Today |access-date=19 February 2011}}
The star's apparent magnitude, or how bright it appears from Earth's perspective, is 9.71. Therefore, it is too dim to be seen with the naked eye.{{Citation needed|date=January 2024}}
=Orbit=
Kepler-37b orbits its parent star at a distance of about 15 million kilometers (9.3 million miles), with a period of roughly 13 days at a distance of 0.1 AU (compared to Mercury's distance from the Sun, which is about 0.38 AU). The outer two planets in the system have orbital periods within one percent of the 8:5 and 3:1 resonances with Kepler-37b's period.
Discovery
Kepler-37b, along with two other planets, Kepler-37c and Kepler-37d, were discovered by the Kepler space telescope, which observes stellar transits. After observing transits of Kepler-37b, astronomers had to compare it with the size of the parent star.
The size of the star was obtained using asteroseismology; Kepler-37 is currently the smallest star to be studied using this process. This allowed the size of Kepler-37b to be determined "with extreme accuracy".
To date, Kepler-37b is the smallest planet discovered around a main-sequence starThe pulsar planet PSR B1257+12 A has a comparable mass. The actual size of PSR B1257+12 A is unknown, but is likely comparable to Kepler-37b. outside the Solar System. Detection of Kepler-37b was possible due to its short orbital period, relative brightness, and low activity of its host star, allowing brightness data to average out quickly.{{cite web|url=http://www.centauri-dreams.org/?p=26604|title=Small Planets Confirm Kepler's Capabilities|website=www.centauri-dreams.org|access-date=5 October 2017}} The discovery of Kepler-37b has led Jack Lissauer, a scientist at NASA's Ames Research Center, to conjecture that "such little planets are common".
See also
Notes
{{reflist|group=lower-alpha}}
References
{{reflist|refs=
{{cite journal |last1=Barclay |first1=T. |last2=Rowe |first2=J. F. |last3=Lissauer |first3=J. J. |last4=Huber |first4=D. |last5=Fressin |first5=F. |last6=Howell |first6=S. B. |last7=Bryson |first7=S. T. |last8=Chaplin |first8=W. J. |last9=Désert |first9=J. M. |title=A sub-Mercury-sized exoplanet |journal=Nature |date=2013-02-20 |issn=0028-0836 |doi=10.1038/nature11914 |arxiv=1305.5587 |bibcode=2013Natur.494..452B |pmid=23426260 |volume=494 |issue=7438 |pages=452–4|s2cid=205232792 }}
{{cite web|url=http://www.nasa.gov/home/hqnews/2013/feb/HQ_13-057_Kepler_Tiny_Planet.html |title=NASA's Kepler Mission Discovers Tiny Planet System |publisher=NASA |date=February 20, 2013 |access-date=February 21, 2013}}
{{cite web|url=http://www.slate.com/blogs/bad_astronomy/2013/02/20/smallest_exoplanet_kepler_37b_is_barely_bigger_than_earth_s_moon.html |title=Astronomers Find the Tiniest Exoplanet Yet |work=Slate |date=February 20, 2013 |access-date=February 21, 2013}}
{{cite journal |last1=Bonomo |first1=A. S. |last2=Dumusque |first2=X. |display-authors=etal |date=April 2023 |title=Cold Jupiters and improved masses in 38 Kepler and K2 small-planet systems from 3661 high-precision HARPS-N radial velocities. No excess of cold Jupiters in small-planet systems |journal=Astronomy & Astrophysics |volume= |issue= |pages= |doi= 10.1051/0004-6361/202346211|arxiv=2304.05773|s2cid=258078829 }}
}}
{{s-start}}
{{s-ach|rec}}
{{s-bef
| before = PSR B1257+12 A
}}
{{s-ttl
| title = Least massive exoplanet{{citation needed|date=March 2014}}
| years = 2013—2015
}}
{{s-aft
| after = WD 1145+017 b
}}
{{s-bef
| before = Kepler-42 d
}}
{{s-ttl
| title = Smallest-radius exoplanet
| years = 2013—2015
}}
{{s-aft
| after = WD 1145+017 b
}}
{{s-end}}
{{Kepler-37}}
{{Exoplanets}}
{{2013 in space}}
{{Sky|18|56|14.32|+|44|31|05.3}}
Category:Exoplanets discovered in 2013