Protoplanet Explained

A protoplanet is a large planetary embryo that originated within a protoplanetary disk and has undergone internal melting to produce a differentiated interior. Protoplanets are thought to form out of kilometer-sized planetesimals that gravitationally perturb each other's orbits and collide, gradually coalescing into the dominant planets.

The planetesimal hypothesis

A planetesimal is an object formed from dust, rock, and other materials, measuring from meters to hundreds of kilometers in size. According to the Chamberlin–Moulton planetesimal hypothesis and the theories of Viktor Safronov, a protoplanetary disk of materials such as gas and dust would orbit a star early in the formation of a planetary system. The action of gravity on such materials form larger and larger chunks until some reach the size of planetesimals.[1] [2]

It is thought that the collisions of planetesimals created a few hundred larger planetary embryos. Over the course of hundreds of millions of years, they collided with one another. The exact sequence whereby planetary embryos collided to assemble the planets is not known, but it is thought that initial collisions would have replaced the first "generation" of embryos with a second generation consisting of fewer but larger embryos. These in their turn would have collided to create a third generation of fewer but even larger embryos. Eventually, only a handful of embryos were left, which collided to complete the assembly of the planets proper.[3]

Early protoplanets had more radioactive elements,[4] the quantity of which has been reduced over time due to radioactive decay. Heating due to radioactivity, impact, and gravitational pressure melted parts of protoplanets as they grew toward being planets. In melted zones their heavier elements sank to the center, whereas lighter elements rose to the surface. Such a process is known as planetary differentiation. The composition of some meteorites show that differentiation took place in some asteroids.

Evidence in the Solar System

In the case of the Solar System, it is thought that the collisions of planetesimals created a few hundred planetary embryos. Such embryos were similar to Ceres and Pluto with masses of about 1022 to 1023 kg and were a few thousand kilometers in diameter.

According to the giant impact hypothesis, the Moon formed from a colossal impact of a hypothetical protoplanet called Theia with Earth, early in the Solar System's history.

In the inner Solar System, the three protoplanets to survive more-or-less intact are the asteroids Ceres, Pallas, and Vesta. Psyche is likely the survivor of a violent hit-and-run with another object that stripped off the outer, rocky layers of a protoplanet.[5] The asteroid Metis may also have a similar origin history to that of Psyche.[6] The asteroid Lutetia also has characteristics that resemble a protoplanet.[7] [8] Kuiper-belt dwarf planets have also been referred to as protoplanets.[9] Because iron meteorites have been found on Earth, it is deemed likely that there once were other metal-cored protoplanets in the asteroid belt that since have been disrupted and that are the source of these meteorites.

Extrasolar protoplanets

In February 2013 astronomers made the first direct observation of a candidate protoplanet forming in a disk of gas and dust around a distant star, HD 100546.[10] [11] Subsequent observations suggest that several protoplanets may be present in the gas disk.[12]

Another protoplanet, AB Aur b, may be in the earliest observed stage of formation for a gas giant. It is located in the gas disk of the star AB Aurigae. AB Aur b is among the largest exoplanets identified, and has a distant orbit, three times as far as Neptune is from the Earth's sun. Observations of AB Aur b may challenge conventional thinking about how planets are formed. It was viewed by the Subaru Telescope and the Hubble Space Telescope.[13]

Rings, gaps, spirals, dust concentrations and shadows in protoplanetary disks could be caused by protoplanets. These structures are not completely understood and are therefore not seen as a proof for the presence of a protoplanet.[14] One new emerging way to study the effect of protoplanets on the disk are molecular line observations of protoplanetary disks in the form of gas velocity maps. HD 97048 b is the first protoplanet detected by disk kinematics in the form of a kink in the gas velocity map.[15]

List of confirmed protoplanets (described as "protoplanets" in literature)!Star!Exoplanet!Mass!Period(yr)!separation(AU)!Distance to earth(parsec)!Year of Discovery!Detection technique
PDS 70PDS 70 b3±111920±2112[16] 2018[17] Direct Imaging
PDS 70 c8±4227[18] 1122019Direct Imaging
HD 97048HD 97048 b2.5±0.59561301842019[19] Disk Kinematics
HD 169142HD 169142 b3±216737.2±1.51142014[20] /2023[21] Direct imaging[22]

Unconfirmed protoplanets

The confident detection of protoplanets is difficult. Protoplanets usually exist in gas-rich protoplanetary disks. Such disks can produce over-densities by a process called disk fragmentation. Such fragments can be small enough to be unresolved and mimic the appearance of a protoplanet.[23] A number of unconfirmed protoplanet candidates are known and some detections were later questioned.

List of unconfirmed/disputed/refuted protoplanets!Star!Exoplanet!Mass!Period(yr)!separation(AU)!Distance to earth(parsec)!Year of Discovery!disputed/unconfirmed/refuted!Detection technique
LkCa 15LkCa 15 b12.72012[24] refuted in 2019[25] Direct imaging
LkCa 15 c18.62015[26] Direct imaging
LkCa 15 d24.72015Direct imaging
HD 100546HD 100546 b4-13[27] 24953±21082015[28] disputed in 2017[29] Direct imaging
AB AurigaeAB Aur b994±491562022[30] disputed in 2023[31] and 2024[32] Direct imaging
Gomez's HamburgerGoHam b0.8-11.4350±502502015[33] unconfirmed candidateDirect imaging
IM Lupi2-31102022[34] unconfirmed candidateDisk Kinematics
HD 163296multiple?[35] 2022[36] unconfirmed candidatesDisk Kinematics
Elias 2-242-5522023[37] unconfirmed candidateDirect imaging + Disk Kinematics

See also

External links

Notes and References

  1. Web site: Cessna . Abby . Planetesimals . Universe Today . 5 April 2022 . 26 July 2009.
  2. Ahrens . T J . Impact Erosion of Terrestrial Planetary Atmospheres . Annual Review of Earth and Planetary Sciences . 1 May 1993 . 21 . 1 . 525–555 . 10.1146/annurev.ea.21.050193.002521 . 1993AREPS..21..525A . 5 April 2022 . 0084-6597. 2060/19920021677 . free .
  3. Book: McBride, Neil. An Introduction to the Solar System. 56. Iain Gilmour . Philip A. Bland . Elaine A. Moore . Mike Widdowson . Ian Wright . Cambridge University Press. Cambridge. 2004. 9780521837354.
  4. Web site: Protoplanets. Abby. Cessna. 2009. Universe Today.
  5. Web site: NASA Selects Investigations for Future Key Planetary Mission. 30 September 2015 .
  6. Kelley . Michael S. Michael J. Gaffey. 9 Metis and 113 Amalthea: A Genetic Asteroid Pair. Icarus. 144 . 1 . 27–38 . 2000. 10.1006/icar.1999.6266 . 2000Icar..144...27K.
  7. Web site: BIG PIC: 2 Pallas, the Asteroid with Protoplanetary Attitude. Discovery Space. Discovery Communications. 2009-10-08. 2009-10-08.
  8. Web site: Klotz. Irene. ASTEROID FAILS TO MAKE IT BIG: A newly studied asteroid is actually a planetary building block that stopped growing.. Discovery News. Discovery Communications. 2011-10-27. 2011-10-27.
  9. Web site: 2009-10-08. Protoplanet frozen in time. MSNBC. Alan Boyle. https://web.archive.org/web/20091010023833/http://cosmiclog.msnbc.msn.com/archive/2009/10/08/2092402.aspx. dead. 2009-10-10. 2009-09-12.
  10. Web site: The Birth of a Giant Planet?. European Southern Observatory. 28 February 2013. 2 March 2013.
  11. Quanz, Sasch P.. 4. Amara, Adam. Meyer, Michael P.. Kenworthy, Matthew P.. Kasper, Markus. Girard, Julien H.. 2013. A young protoplanet candidate embedded in the circumstellar disk of HD 100546. Astrophysical Journal. 766. 1. L1. 10.1088/2041-8205/766/1/l1. 1302.7122 . 2013ApJ...766L...1Q . 56140977.
  12. Garufi . A. . Quanz . S. P. . Schmid . H. M. . Mulders . G. D. . Avenhaus . H. . Boccaletti . A. . Ginski . C. . Langlois . M. . Stolker . T. . Augereau . J.-C. . Benisty . M. . Lopez . B. . Dominik . C. . Gratton . R. . Henning . T. . Janson . M. . Ménard . F. . Meyer . M. R. . Pinte . C. . Sissa . E. . Vigan . A. . Zurlo . A. . Bazzon . A. . Buenzli . E. . Bonnefoy . M. . Brandner . W. . Chauvin . G. . Cheetham . A. . Cudel . M. . Desidera . S. . Feldt . M. . Galicher . R. . Kasper . M. . Lagrange . A.-M. . Lannier . J. . Maire . A. L. . Mesa . D. . Mouillet . D. . Peretti . S. . Perrot . C. . Salter . G. . Wildi . F. . The SPHERE view of the planet-forming disk around HD 100546 . Astronomy & Astrophysics . April 2016 . 588 . A8 . 10.1051/0004-6361/201527940 . 5 April 2022 . en . 0004-6361. free . 1601.04983 . 2016A&A...588A...8G .
  13. News: Gigantic Jupiter-like alien planet observed still 'in the womb' . 5 April 2022 . CBC News . April 5, 2022.
  14. Pinte . Christophe . Teague . Richard . Flaherty . Kevin . Hall . Cassandra . Facchini . Stefano . Casassus . Simon . 2022-03-01 . Kinematic Structures in Planet-Forming Disks . Protostars and Planets VII . 534 . 645 . 2203.09528 . 2023ASPC..534..645P .
  15. Pinte . C. . van der Plas . G. . Ménard . F. . Price . D. J. . Christiaens . V. . Hill . T. . Mentiplay . D. . Ginski . C. . Choquet . E. . Boehler . Y. . Duchêne . G. . Perez . S. . Casassus . S. . 2019-08-01 . Kinematic detection of a planet carving a gap in a protoplanetary disk . Nature Astronomy . 3 . 12 . 1109–1114 . 10.1038/s41550-019-0852-6 . 1907.02538 . 2019NatAs...3.1109P . 195820690 . 2397-3366.
  16. Gaia Collaboration . 2020-11-01 . VizieR Online Data Catalog: Gaia EDR3 (Gaia Collaboration, 2020) . VizieR Online Data Catalog . I/350 . 10.26093/cds/vizier.1350 . 2020yCat.1350....0G.
  17. Web site: PDS 70 NASA Exoplanet Archive . 2023-03-01 . exoplanetarchive.ipac.caltech.edu.
  18. Web site: Orbital Period Calculator Binary System . 2023-03-01 . www.omnicalculator.com . en.
  19. Web site: HD 97048 NASA Exoplanet Archive . 2023-03-01 . exoplanetarchive.ipac.caltech.edu.
  20. Reggiani . Maddalena . Quanz . Sascha P. . Meyer . Michael R. . Pueyo . Laurent . Absil . Olivier . Amara . Adam . Anglada . Guillem . Avenhaus . Henning . Girard . Julien H. . Carrasco Gonzalez . Carlos . Graham . James . Mawet . Dimitri . Meru . Farzana . Milli . Julien . Osorio . Mayra . 2014-09-01 . Discovery of a Companion Candidate in the HD 169142 Transition Disk and the Possibility of Multiple Planet Formation . The Astrophysical Journal . 792 . 1 . L23 . 1408.0813 . 2014ApJ...792L..23R . 10.1088/2041-8205/792/1/L23 . 0004-637X . 37427761.
  21. Web site: HD 169142 NASA Exoplanet Archive . 2023-04-11 . exoplanetarchive.ipac.caltech.edu.
  22. Hammond . Iain . Christiaens . Valentin . Price . Daniel J. . Toci . Claudia . Pinte . Christophe . Juillard . Sandrine . Garg . Himanshi . 2023-02-01 . Confirmation and Keplerian motion of the gap-carving protoplanet HD 169142 b . Monthly Notices of the Royal Astronomical Society . 522 . 1 . L51–L55 . 2302.11302 . 2023MNRAS.522L..51H . 10.1093/mnrasl/slad027. free .
  23. Teague . Richard . Jankovic . Marija R. . Haworth . Thomas J. . Qi . Chunhua . Ilee . John D. . 2020-06-01 . A three-dimensional view of Gomez's hamburger . Monthly Notices of the Royal Astronomical Society . 495 . 1 . 451–459 . 10.1093/mnras/staa1167 . free . 2003.02061 . 2020MNRAS.495..451T . 0035-8711.
  24. Kraus . Adam L. . Ireland . Michael J. . 2012-01-01 . LkCa 15: A Young Exoplanet Caught at Formation? . The Astrophysical Journal . 745 . 1 . 5 . 10.1088/0004-637X/745/1/5 . 1110.3808 . 2012ApJ...745....5K . 0004-637X.
  25. Currie . Thayne . Marois . Christian . Cieza . Lucas . Mulders . Gijs D. . Lawson . Kellen . Caceres . Claudio . Rodriguez-Ruiz . Dary . Wisniewski . John . Guyon . Olivier . Brandt . Timothy D. . Kasdin . N. Jeremy . Groff . Tyler D. . Lozi . Julien . Chilcote . Jeffrey . Hodapp . Klaus . 2019-05-01 . No Clear, Direct Evidence for Multiple Protoplanets Orbiting LkCa 15: LkCa 15 bcd are Likely Inner Disk Signals . The Astrophysical Journal . 877 . 1 . L3 . 10.3847/2041-8213/ab1b42 . free . 1905.04322 . 2019ApJ...877L...3C . 0004-637X.
  26. Sallum . S. . Follette . K. B. . Eisner . J. A. . Close . L. M. . Hinz . P. . Kratter . K. . Males . J. . Skemer . A. . Macintosh . B. . Tuthill . P. . Bailey . V. . Defrère . D. . Morzinski . K. . Rodigas . T. . Spalding . E. . 2015-11-01 . Accreting protoplanets in the LkCa 15 transition disk . Nature . 527 . 7578 . 342–344 . 10.1038/nature15761 . 26581290 . 1511.07456 . 2015Natur.527..342S . 916170 . 0028-0836.
  27. Quanz . Sascha P. . Amara . Adam . Meyer . Michael R. . Girard . Julien H. . Kenworthy . Matthew A. . Kasper . Markus . 2015-07-01 . Confirmation and Characterization of the Protoplanet HD 100546 b—Direct Evidence for Gas Giant Planet Formation at 50 AU . The Astrophysical Journal . 807 . 1 . 64 . 1412.5173 . 2015ApJ...807...64Q . 10.1088/0004-637X/807/1/64 . 1887/48578 . 0004-637X . 119119314.
  28. Web site: HD 100546 NASA Exoplanet Archive . 2023-03-01 . exoplanetarchive.ipac.caltech.edu.
  29. Rameau . Julien . Follette . Katherine B. . Pueyo . Laurent . Marois . Christian . Macintosh . Bruce . Millar-Blanchaer . Maxwell . Wang . Jason J. . Vega . David . Doyon . René . Lafrenière . David . Nielsen . Eric L. . Bailey . Vanessa . Chilcote . Jeffrey K. . Close . Laird M. . Esposito . Thomas M. . 2017-06-01 . An Optical/Near-infrared Investigation of HD 100546 b with the Gemini Planet Imager and MagAO . The Astronomical Journal . 153 . 6 . 244 . 1704.06317 . 2017AJ....153..244R . 10.3847/1538-3881/aa6cae . 0004-6256 . 19100982 . free.
  30. Web site: AB Aur NASA Exoplanet Archive . 2023-03-01 . exoplanetarchive.ipac.caltech.edu.
  31. Zhou . Yifan . Bowler . Brendan P. . Yang . Haifeng . Sanghi . Aniket . Herczeg . Gregory J. . Kraus . Adam L. . Bae . Jaehan . Long . Feng . Follette . Katherine B. . Ward-Duong . Kimberley . Zhu . Zhaohuan . Biddle . Lauren I. . Close . Laird M. . Yushu Jiang . Lillian . Wu . Ya-Lin . 30 Aug 2023 . UV-Optical Emission of AB Aur b is Consistent with Scattered Stellar Light . Astrophysical Journal . 166 . 6 . 11 . 2308.16223 . 2023AJ....166..220Z . 10.3847/1538-3881/acf9ec . free.
  32. Biddle . Lauren I. . Bowler . Brendan P. . Zhou . Yifan . Franson . Kyle . Zhang . Zhoujian . 2024-04-01 . Deep Paβ Imaging of the Candidate Accreting Protoplanet AB Aur b . The Astronomical Journal . 167 . 4 . 172 . 2402.12601 . 2024AJ....167..172B . 10.3847/1538-3881/ad2a52 . free . 0004-6256.
  33. Berné . O. . Fuente . A. . Pantin . E. . Bujarrabal . V. . Baruteau . C. . Pilleri . P. . Habart . E. . Ménard . F. . Cernicharo . J. . Tielens . A. G. G. M. . Joblin . C. . 2015-06-01 . Very Large Telescope observations of Gomez's Hamburger: Insights into a young protoplanet candidate . Astronomy and Astrophysics . 578 . L8 . 10.1051/0004-6361/201526041 . 1504.02735 . 2015A&A...578L...8B . 0004-6361.
  34. Verrios . Harrison J. . Price . Daniel J. . Pinte . Christophe . Hilder . Thomas . Calcino . Josh . 2022-07-01 . Kinematic Evidence for an Embedded Planet in the IM Lupi Disk . The Astrophysical Journal . 934 . 1 . L11 . 2207.02869 . 2022ApJ...934L..11V . 10.3847/2041-8213/ac7f44 . 0004-637X . free.
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  37. Pinte . C. . Hammond . I. . Price . D. J. . Christiaens . V. . Andrews . S. M. . Chauvin . G. . Pérez . L. M. . Jorquera . S. . Garg . H. . Norfolk . B. J. . Calcino . J. . Bonnefoy . M. . 2023-11-01 . Kinematic and thermal signatures of the directly imaged protoplanet candidate around Elias 2-24 . Monthly Notices of the Royal Astronomical Society . 526 . 1 . L41–L46 . 10.1093/mnrasl/slad010 . free . 2301.08759 . 2023MNRAS.526L..41P . 0035-8711.

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