2009 SH2

{{Short description|Near-Earth asteroid}} {{DISPLAYTITLE:{{mp|2009 SH|2}}}} {{Use dmy dates|date=February 2021}} {{Infobox planet | minorplanet = yes | name = {{mp|2009 SH|2}} | background = #FFC2E0 | image = | image_size = | caption = | discovery_ref = <ref name="MPEC-2009-S51"/><ref name="MPC-object"/> | discoverer = [[Siding Spring Survey]] | discovery_site = [[Siding Spring Observatory|Siding Spring Obs.]] | discovered = 18 September 2009 | mpc_name = {{mp|2009 SH|2}} | alt_names = | pronounced = | named_after = | mp_category = {{nowrap|Earth [[co-orbital]]<ref name="Marcos2013"/>{{·}}[[Near-Earth object|NEO]]<br/>[[Aten asteroid|Aten]]<ref name="jpldata"/>}} | orbit_ref = <ref name="jpldata"/> | epoch = 21 November 2025 ([[Julian day|JD]] 2461000.5) | uncertainty = 4 | observation_arc = 14 days | earliest_precovery_date = | aphelion = 1.085 [[Astronomical unit|AU]] | perihelion = 0.8978 AU | time_periastron = 21 October 2025 05:40 UT | semimajor = 0.991 AU | eccentricity = 0.09423 | period = 0.99 yr (360.47 d) | mean_anomaly = 30.7234[[Degree (angle)|°]] | mean_motion = {{Deg2DMS|0.9986873|sup=ms}} / day | inclination = 6.810° | asc_node = 6.657° | arg_peri = 101.752° | moid = {{cvt|0.0002|AU|km}} | mean_diameter = {{val|30|-|60|ul=m}} {{small|(assumed [[geometric albedo|albedo]] 0.05–0.25)}}<ref name="sizemagnitude"/> | rotation = {{val|1.26|ul=h}}<ref name="jpldata"/> | albedo = | spectral_type = | magnitude = 18.8 {{small|(at discovery)}}<ref name="MPEC-2009-S51"/> | abs_magnitude = 24.9<ref name="jpldata"/><ref name="MPC-object"/> }}

'''{{mp|2009 SH|2}}''' is a sub-kilometer [[near-Earth asteroid]] of the [[Aten asteroid|Aten group]], discovered by the [[Siding Spring Survey]] at [[Siding Spring Observatory]], [[Australia]] on 18 September 2009. It is in a [[co-orbital configuration]] with Earth, a type of 1:1 [[orbital resonance]] where the asteroid appears to [[Libration|librate]] around Earth's path in a [[horseshoe orbit]] when viewed in a [[Rotating reference frame|corotating reference frame]] with Earth. The co-orbital state of {{mp|2009 SH|2}} is only temporary as it has entered it about 30 years ago and will leave it in about 100 years into the future.<ref name="Marcos2013"/>

== Discovery == {{mp|2009 SH|2}} was discovered by the [[Siding Spring Survey]] at [[Siding Spring Observatory]], [[Coonabarabran, New South Wales]], [[Australia]] on 18 September 2009. It was first observed in the [[constellation]] [[Fornax]] at an [[apparent magnitude]] of 18.8.<ref name="MPEC-2009-S51"/> The asteroid was moving at an on-sky rate around 2.5 [[arcseconds]] per minute, from a distance of {{convert|0.030|AU|e6km e6mi|abbr=unit}} from Earth.<ref name="NEODyS-Eph-Dis"/> Follow-up observations of the asteroid were carried out by the Rio Cuarto Observatory {{small|([[List of observatory codes#I20|I20]])}} on the following day. The asteroid was then confirmed by the [[Minor Planet Center]] and announced as {{mp|2009 SH|2}} on 19 September 2009.<ref name="MPEC-2009-S51"/>

== Orbit == [[File:2009 SH2 Orbit Comparision with Earth.png|thumb|left|Orbit diagram of {{mp|2009 SH|2}} and the inner planets]] {{mp|2009 SH|2}} orbits the Sun at an average distance of 0.99 [[Astronomical unit|AU]] once every 360 days, or approximately 0.99 years. Its orbit has an [[orbital eccentricity|eccentricity]] of 0.09 and an [[orbital inclination|inclination]] of 7[[Degree (angle)|°]] with respect to the [[ecliptic]] plane. Over the course of its orbit, its distance from the Sun ranges from 0.90 AU at [[perihelion]] to 1.08 AU at [[aphelion]], crossing the orbit of [[Earth]]. Since its orbit crosses that of Earth's while having a [[semi-major axis]] less than 1 AU, {{mp|2009 SH|2}} is classified as an [[Aten asteroid]]. Its nominal orbit has a small [[minimum orbit intersection distance]] approximately {{cvt|0.0006|AU|km mi}} from Earth's orbital path and periodically makes close approaches to Earth.<ref name="jpldata"/>

In 2013, astronomers Carlos and Raúl de la Fuente Marcos identified {{mp|2009 SH|2}} to be in a [[co-orbital configuration]] with Earth, a type of 1:1 [[orbital resonance]] where the asteroid appears to librate around Earth's path in a [[horseshoe orbit]] when viewed in a [[Rotating reference frame|corotating reference frame]] with Earth. The co-orbital state of {{mp|2009 SH|2}} is only temporary as it has entered it about 30 years ago and will leave it in about 100 years into the future.<ref name="Marcos2013"/>

== Physical characteristics == Based on a magnitude-to-diameter conversion and a measured [[absolute magnitude]] of 24.9, {{mp|2009 SH|2}} measures between 30 and 60 meters in diameter for an assumed [[geometric albedo]] of 0.25 and 0.05, respectively.<ref name="MPC-object"/><ref name="sizemagnitude"/> A rotation period of {{val|1.26|u=h}} has been tentatively measured from its [[lightcurve]].<ref name="jpldata"/>

== See also == * [[Arjuna asteroid]] * {{mpl|2003 YN|107}} * {{mpl|2006 JY|26}} * {{mpl|2012 FC|71}} * {{mpl|2013 BS|45}}

== References == <references>

<ref name="jpldata">{{cite web |type = 2009-10-02 last obs. |title = JPL Small-Body Database Browser: 2009 SH2 |url = https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3467258 |publisher = [[Jet Propulsion Laboratory]] |accessdate = 12 February 2021}}</ref>

<ref name="MPC-object">{{cite web |title = 2009 SH2 |url = http://www.minorplanetcenter.net/db_search/show_object?object_id=2009+SH2 |work = Minor Planet Center |publisher = International Astronomical Union |accessdate = 12 February 2021}}</ref>

<ref name="NEODyS-Eph-Dis">{{cite web |type = Ephemerides at discovery (obs. code E12) |title = 2009SH2 Ephemerides |url = https://newton.spacedys.com/neodys/index.php?pc=1.1.3.1&n=2009SH2&oc=E12&y0=2009&m0=9&d0=18&h0=18&mi0=0&y1=2009&m1=9&d1=18&h1=19&mi1=0&ti=10&tiu=minutes |work = Near Earth Objects – Dynamic Site |publisher = Department of Mathematics, University of Pisa, Italy |accessdate = 12 February 2021}}</ref>

<ref name="MPEC-2009-S51">{{cite web |title = MPEC 2009-S51 : 2009 SH2 |url = https://minorplanetcenter.net/mpec/K09/K09S51.html |work = Minor Planet Electronic Circular |publisher = [[Minor Planet Center]] |date = 19 September 2009 |accessdate = 12 February 2021}}</ref>

<ref name="sizemagnitude">{{cite web |title = Conversion of Absolute Magnitude to Diameter for Minor Planets |url = http://www.physics.sfasu.edu/astro/asteroids/sizemagnitude.html |first = Dan |last = Bruton |work = Department of Physics, Engineering, and Astronomy |publisher = Stephen F. Austin State University |accessdate = 12 February 2021 |archive-date = 23 July 2011 |archive-url = https://web.archive.org/web/20110723191750/http://www.physics.sfasu.edu/astro/asteroids/sizemagnitude.html |url-status = dead }}</ref>

<ref name="Marcos2013">{{cite journal |first1 = C. |last1 = de la Fuente Marcos |first2 = R. |last2 = de la Fuente Marcos |title = A resonant family of dynamically cold small bodies in the near-Earth asteroid belt |date = September 2013 |journal = Monthly Notices of the Royal Astronomical Society: Letters |volume = 434 |issue = 1 |pages = L1–L5 |doi = 10.1093/mnrasl/slt062 |doi-access = free |arxiv = 1305.2825 |bibcode = 2013MNRAS.434L...1D}}</ref>

</references>

== External links == * {{NeoDys|2009sh2}} * {{ESA-SSA|2009SH2}} * {{JPL small body|id=3467258}}

{{Small Solar System bodies}}  {{Portal bar|Astronomy|Outer Space}}

{{DEFAULTSORT:2009 SH2}} [[Category:Aten asteroids|#]] [[Category:Discoveries by SSS|#]] [[Category:Minor planet object articles (unnumbered)]] [[Category:Earth co-orbital asteroids|#]] [[Category:Earth-crossing asteroids]] [[Category:Astronomical objects discovered in 2009|20090918]]