Michael Efroimsky

{{short description|American astronomer of Russian origin|bot=PearBOT 5}}

{{Use dmy dates|date=January 2024}}

Michael Efroimsky ({{langx|ru| Михаил Эфроимский}}) is an American astronomer of Russian origin.

His research interests are in celestial mechanics and Planetary Science.

He is working as a Research Scientist at the US Naval Observatory in Washington DC.

Michael Efroimsky is a member of the International Astronomical Union and the American Astronomical Society (AAS).

In 2008 - 2009, he served as the Chair of the Division on Dynamical Astronomy of the AAS.

With Sergei Kopeikin and George Kaplan, Michael Efroimsky co-authored a book{{cite book

|last1=Kopeikin |first1=S.

|author2=Efroimsky M. |author3=Kaplan G.

|name-list-style=amp |date=2011

|title=Relativistic Celestial Mechanics of the Solar System.

|publisher=Wiley-VCH, Berlin

|isbn=978-3-527-40856-6

|url=https://books.google.com/books?id=uN5_DQWSR14C

}} on the relativistic celestial mechanics of the Solar System.

With Benoit Noyelles, Julien Frouard and Valeri V. Makarov, Michael Efroimsky co-authored a theory

{{cite journal

|last1= Noyelles

|first1= Benoit

|last2= Frouard

|first2= Julien

|last3= Makarov

|first3= Valeri V.

|last4= Efroimsky

|first4= Michael

|date=October 2014

|title= Spin-orbit evolution of Mercury revisited

|journal= Icarus

|volume= 241

|pages= 26–44

|bibcode = 2014Icar..241...26N

|doi= 10.1016/j.icarus.2014.05.045

|arxiv= 1307.0136

|s2cid= 53690707

}}

explaining the origin of the present state of rotation of the planet Mercury, a so-called 3:2 spin-orbit resonance.

With Amirhossein Bagheri, Amir Khan, and other colleagues, Michael Efroimsky co-authored a theory explaining the origin and orbital evolution of Phobos and Deimos, the satellites of Mars.

{{cite journal

|last= A. Bagheri, A. Khan, M. Efroimsky, M. Kruglyakov, and D. Giardini

|date= 22 February 2021

|title= Dynamical evidence for Phobos and Deimos as remnants of a disrupted common progenitor .

|journal= Nature Astronomy

|volume= 5

|issue= 6

|pages= 539–543

|doi= 10.1038/s41550-021-01306-2

|bibcode= 2021NatAs...5..539B

|s2cid= 233924981

|url= https://doi.org/10.1038/s41550-021-01306-2

}}

According to this theory, Phobos and Deimos are remnants of a common progenitor, a larger protomoon destroyed by a collision with a planetesimal.

In 2024, Michael Efroimsky published a paper outlining the hypothesis to explain the unique shape of Mars. He suggested that the high triaxiality of this planet is due to a long-lost moon, which was synchronous, i.e., residing above the same point of the Martial equator. Efroimsky christened it Nerio.

{{cite journal

|last= M. Efroimsky

|date= 17 October 2024

|title= A Synchronous Moon as a Possible Cause of Mars' Initial Triaxiality

|journal= Journal of Geophysical Research: Planets

|volume= 129

|issue= 10

|pages= E2023JE008277

|doi= 10.1029/2023JE008277

|arxiv= 2408.14725

|bibcode= 2024JGRE..12908277E

|url= https://doi.org/10.1029/2023JE008277

}}

He demonstrated that if Nerio were large enough, perhaps a third the mass of our Moon, its gravitational pull on the young and still soft Mars was sufficient to create an asymmetric tidal bulge, which later fossilised and made the equator noncircular, resulting in the planet's triaxial shape. Efroimsky also hypothesised that the tips of that bulge were more prone to subsequent volcanic and tectonic activity than the rest of the Martian surface, leading to the development of both Tharsis and the highlands on the side opposite to it.

Michael Efroimsky also published translations from classical Russian poetry.

{{cite journal

|last= Efroimsky

|first= Michael

|date=October 2018

|title= Translations from classical Russian poetry. Three poems by Osip Mandelstam.

|journal= Delos: A Journal of Translation and World Literature

|volume= 33

|number = 2

|pages= 202–209

|url= http://journals.upress.ufl.edu/delos/article/view/761

}}

{{cite journal

|last= Efroimsky

|first= Michael

|date=October 2018

|title= Translations from classical Russian poetry. Two poems by Joseph Brodsky.

|journal= Delos: A Journal of Translation and World Literature

|volume= 33

|number = 2

|pages= 210–218

|url= http://journals.upress.ufl.edu/delos/article/view/762

}}