2008 HJ

{{Short description|Asteroid}}

{{Use dmy dates|date=February 2018}}

{{Infobox planet

| minorplanet = yes

| background = #FFC2E0

| name = {{mp|2008 HJ}}

| image =

| caption =

| discovery_ref =

| discoverer = LINEAR

| discovery_site = Lincoln Lab ETS

| discovered = 24 April 2008

| mpc_name = {{mp|2008 HJ|}}

| mp_category = NEO{{·}}Apollo

| orbit_ref =

| epoch = 13 January 2016 (JD 2457400.5)

| aphelion = {{Convert|2.29553|AU|Gm|abbr=on|lk=on}} (Q)

| perihelion = {{Convert|0.968318|AU|Gm|abbr=on}} (q)

| semimajor = {{Convert|1.63192|AU|Gm|abbr=on}} (a)

| eccentricity = 0.40664 (e)

| period = 2.08 yr (761.46 d)

| mean_anomaly = 237.912° (M)

| inclination = 0.925579° (i)

| asc_node = 47.4700° (Ω)

| arg_peri = 204.1346° (ω)

| dimensions = 12×24 m

| mass = 5 million kg (assumed)

| albedo =

| spectral_type =

| sidereal_day = {{Convert|0.01185|h|s|abbr=on|lk=on|disp=flip}}

| abs_magnitude = 25.8

| mean_motion = {{Deg2DMS|0.472775|sup=ms}} /day (n)

| uncertainty = 6

| moid = {{Convert|0.00170917|AU|km|abbr=on}}

| jupiter_moid = {{Convert|2.75111|AU|Gm|abbr=on}}

}}

2008 HJ is a sub-kilometer asteroid, classified as near-Earth object of the Apollo group.

It was discovered by Lincoln Laboratory ETS, New Mexico. Observers M. Bezpalko, D. Torres, R. Kracke, G. Spitz, J. Kistler. Richard Miles using the Faulkes Telescope South at Siding Spring Observatory, Australia determined that the asteroid rotates rapidly. It measures only 12 m by 24 m and is very dense, having a mass of about 5,000 tonnes. If the asteroid were not dense, it is probable that the rapid rotation would cause the asteroid to disrupt and fly apart.

At the time of discovery, {{mp|2008 HJ}} had the smallest known rotation period in the Solar System, completing one revolution every 42.7 seconds.

It is listed on the Sentry Risk Table with a 1 in 17,000 chance of impacting Earth on May 2, 2081. An impact from this object would be comparable to the Chelyabinsk meteor.