ʻOumuamua: Difference between revisions

[[File:Artist's impression of {{okina}}Oumuamua.jpg|thumb|Artist's impression of {{okina}}Oumuamua]]A 2019 paper finds the best models as either a cigar-shape, 1:8 aspect ratio, or disc-shape, 1:6 aspect ratio, with the disc more likely since its rotation does not require a specific orientation to see the range of brightnesses observed.<ref name="Mashchenko2019">{{cite journal |title=Modeling the light curve of 'Oumuamua: evidence for torque and disc-like shape |journal=Monthly Notices of the Royal Astronomical Society |first=Sergey |last=Mashchenko |s2cid=182952355 |volume=489 |issue=3 |pages=3003–3021 |date=November 2019 |doi=10.1093/mnras/stz2380 |doi-access=free |bibcode=2019MNRAS.489.3003M |arxiv=1906.03696}}</ref> [[Monte Carlo method|Monte Carlo simulations]] based on the available orbit determination suggest that the equatorial [[Axial tilt|obliquity]] of {{okina}}Oumuamua could be about 93 degrees, if it has a very prolate or cigar-like shape, or close to 16 degrees, if it is very oblate or disk-like.<ref name="rotationpole">{{cite journal |last1=de la Fuente Marcos |first1=C. |last2=de la Fuente Marcos |first2=R. |title=Constraining the orientation of the spin axes of extrasolar minor bodies 1I/2017 U1 ('Oumuamua) and 2I/Borisov |journal=[[Astronomy and Astrophysics]] |volume=643 |pages=A18 (17 pp) |date=1 November 2020 |doi=10.1051/0004-6361/202037447 |arxiv=2009.08423 |bibcode=2020A&A...643A..18D |s2cid=221761422 |url=https://www.aanda.org/articles/aa/abs/2020/11/aa37447-20/aa37447-20.html |access-date=27 October 2020 |archive-date=1 February 2021 |archive-url=https://web.archive.org/web/20210201045557/https://www.aanda.org/articles/aa/abs/2020/11/aa37447-20/aa37447-20.html |url-status=live }}</ref> A 2021 paper foundproposed that, if 'Oumuamua is made of nitrogen ice, the extreme shape wascould likelybe a result of recent evaporation, and that when the object entered the Solar System it likely had an unremarkable 2:1 aspect ratio. The authors calculated that in this scenario, a month after perihelion, that {{okina}}Oumuamua had lost 92% of the mass it had upon entering the Solar System.<ref name="JGRP-20210316a" />

[[Light curve]] observations suggest however that the object may be composed of dense metal-rich rock that has been reddened by millions of years of exposure to [[cosmic ray]]s.<ref name="Rincon2017"/><ref>{{Cite magazine |url=https://www.science.org/content/article/updated-first-time-astronomers-are-tracking-distant-visitor-streaking-through-our-solar |title=Updated: For the first time, astronomers are tracking a distant visitor streaking through our solar system |magazine=Science |first=Paul |last=Voosen |date=20 November 2017 |doi=10.1126/science.aar3433 |access-date=30 November 2017 |archive-date=21 November 2017 |archive-url=https://web.archive.org/web/20171121122550/http://www.sciencemag.org/news/2017/11/updated-first-time-astronomers-are-tracking-distant-visitor-streaking-through-our-solar |url-status=live }}</ref><ref>{{cite web |url=https://www.space.com/38838-interstellar-asteroid-oumuamua-space-cigar.html |title=Wow! 1st Interstellar Asteroid Is a Spinning Space Cigar |first=Ian |last=O'Neill |website=Space.com |date=20 November 2017 |access-date=30 November 2017 |archive-date=25 April 2020 |archive-url=https://web.archive.org/web/20200425005615/https://www.space.com/38838-interstellar-asteroid-oumuamua-space-cigar.html |url-status=live }}</ref> It is thought that its surface contains [[tholin]]s, which are irradiated [[organic compound]]s that are more common in objects in the outer Solar System and can help determine the age of the surface.<ref name=MattWilliams2017-11-20a>{{cite web |first=Matt |last=Williams |url=https://www.universetoday.com/137944/interstellar-asteroid-probably-pretty-strange-looking/ |title=That Interstellar Asteroid is probably pretty strange looking |publisher=[[Universe Today]] |date=20 November 2017 |access-date=20 December 2017 |quote=Its dark and reddened surface is also an indication of tholins, which are the result of organic molecules (like methane) being irradiated by cosmic rays for millions of years. |archive-date=22 December 2017 |archive-url=https://web.archive.org/web/20171222052002/https://www.universetoday.com/137944/interstellar-asteroid-probably-pretty-strange-looking/ |url-status=live }}</ref><ref name="MattWilliams2017-11-24a">{{cite web |last=Williams |first=Matt |date=24 November 2017 |title=Project Lyra, a mission to chase down that interstellar asteroid |url=https://www.universetoday.com/137960/project-lyra-mission-chase-interstellar-asteroid-1/ |url-status=live |archive-url=https://web.archive.org/web/20171230124909/https://www.universetoday.com/137960/project-lyra-mission-chase-interstellar-asteroid-1/ |archive-date=30 December 2017 |access-date=20 December 2017 |publisher=[[Universe Today]] |quote=It was also determined to be rocky and metal rich, and to contain traces of tholins – organic molecules that have been irradiated by UV radiation.}} Also here [https://phys.org/news/2017-11-lyra-mission-interstellar-asteroid.html] {{Webarchive|url=https://web.archive.org/web/20171222052951/https://phys.org/news/2017-11-lyra-mission-interstellar-asteroid.html|date=22 December 2017}} at Phys.org</ref> This possibility is inferred from spectroscopic characterization and its reddish color,<ref name=MattWilliams2017-11-20a /><ref name="Fitzsimmons2017a">{{cite journal |last1=Fitzsimmons |first1=A. |first2=C. |last2=Snodgrass |first3=B. |last3=Rozitis |first4=B. |last4=Yang |first5=M. |last5=Hyland |first6=T. |last6=Seccull |first7=M. T. |last7=Bannister |first8=W. C. |last8=Fraser |first9=R. |last9=Jedicke |first10=P. |last10=Lacerda |s2cid=216937304 |display-authors=1 |title=Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U1 {{okina}}Oumuamua |arxiv=1712.06552 |date=18 December 2017 |journal=Nature Astronomy |volume=2 |issue=2 |page=133 |doi=10.1038/s41550-017-0361-4 |quote=The discovery epoch photometry implies a highly elongated body with radii of ~200×20 m when a comet-like geometric albedo of 0.04 is assumed. Here we report spectroscopic characterisation of {{okina}}Oumuamua, finding it to be variable with time but similar to organically rich surfaces found in the outer Solar System. The observable ISO population is expected to be dominated by comet-like bodies in agreement with our spectra, yet the reported inactivity implies a lack of surface ice. We show this is consistent with predictions of an insulating mantle produced by long-term cosmic ray exposure. An internal icy composition cannot therefore be ruled out by the lack of activity, even though {{okina}}Oumuamua passed within 0.25 au of the Sun. |bibcode=2018NatAs...2..133F |url=https://pure.qub.ac.uk/portal/en/publications/spectroscopy-and-thermal-modelling-of-the-first-interstellar-object-1i2017-u1-oumuamua(433758b2-c945-4038-8c19-b4e5b52ae1e2).html |access-date=25 September 2018 |archive-date=17 October 2019 |archive-url=https://web.archive.org/web/20191017090156/https://pure.qub.ac.uk/portal/en/publications/spectroscopy-and-thermal-modelling-of-the-first-interstellar-object-1i2017-u1-oumuamua(433758b2-c945-4038-8c19-b4e5b52ae1e2).html |url-status=live }}</ref> and from the expected effects of interstellar radiation.<ref name="Fitzsimmons2017a" /> Despite the lack of any [[Coma (cometary)|cometary coma]] when it approached the Sun, it may still contain internal ice, hidden by "an insulating mantle produced by long-term [[cosmic ray]] exposure".<ref name="Fitzsimmons2017a" />