is a sub-kilometer

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

, classified as

near-Earth object A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). ...

and

potentially hazardous asteroid A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and is large enough to cause significant regional damage in the event of impact. They are ...

of the

Apollo group Apollo Education Group, Inc. is an American corporation based in the South Phoenix area of Phoenix, Arizona, with an additional corporate office in Chicago, Illinois. The company owns and operates several higher-learning institutions, including ...

, approximately in diameter. It safely passed 1.27 lunar distances from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

on 31 October 2015 at 17:01 UTC, and passed by Earth again in November 2018.

Discovery

The asteroid was first observed on 10 October 2015 by

Pan-STARRS The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1; List of observatory codes, obs. code: IAU code#F51, F51 and Pan-STARRS2 obs. code: IAU code#F52, F52) located at Haleakala Observatory, Hawaii, US, consists of astronomical c ...

at an apparent magnitude of 20 using a Ritchey–Chrétien telescope. The asteroid was not discovered sooner because it spends most of its time beyond the orbit of

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

, has a large orbital inclination, and is usually well below the

plane of the ecliptic The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic agains ...

. The asteroid last passed within of Earth on 29 October 1923 and will not pass that close again until 1 November 2088. The media has nicknamed the asteroid the "Great Pumpkin" after the animated

Halloween Halloween or Hallowe'en (less commonly known as Allhalloween, All Hallows' Eve, or All Saints' Eve) is a celebration observed in many countries on 31 October, the eve of the Western Christian feast of All Saints' Day. It begins the observanc ...

television special ''

It's the Great Pumpkin, Charlie Brown ''It's the Great Pumpkin, Charlie Brown'' is a 1966 American prime time animated television special based on the comic strip ''Peanuts'' by Charles M. Schulz. A Halloween special, it was the third ''Peanuts'' special (and second holiday-themed ...

'', "Spooky", the "Halloween Asteroid", and the "Skull Asteroid" due to its

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

-like appearance following

radio frequency Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upp ...

images taken at

Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science F ...

and closest approach coincidentally occurring on Halloween day.

2015 flyby

On 31 October 2015 the asteroid passed from the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

and then passed from Earth. The last approach this close by an object with

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse Logarithmic scale, logarithmic Magnitude (astronomy), astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent mag ...

brighter than 20 was on 3 July 2006 at 1.1 lunar distances. The next object this large known to pass this close to Earth is that will pass about 1 lunar distance from Earth on 7 August 2027. It is estimated that there are about 2400 near-Earth asteroids 300–500 meters in diameter, of which about 1100 have been discovered. During closest approach to Earth the asteroid reached about

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

10, which is much too faint to be seen by the naked eye. Even at peak brightness, the asteroid was a challenging target for

amateur astronomer Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the unaided eye, binoculars, or telescopes. Even though scientific research may not be their primary goal, some amateur astronomers ...

s with small telescopes, best seen in the

Northern hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

. The glare from an 80% waning gibbous Moon also hindered observations. At 11:00 UT the asteroid was in the constellation of

Taurus Taurus is Latin for 'bull' and may refer to: * Taurus (astrology), the astrological sign * Taurus (constellation), one of the constellations of the zodiac * Taurus (mythology), one of two Greek mythological characters named Taurus * '' Bos tauru ...

about 9 degrees from the Moon and moving at a rate of 3.4 degrees per hour. At the time of closest approach of 17:00 UT the asteroid was in the constellation of

Ursa Major Ursa Major (; also known as the Great Bear) is a constellation in the northern sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear," referring to and contrasting it with nearby Ursa ...

about 56 degrees from the Moon and moving at a rate of 14.7 degrees per hour. After closest approach it quickly became too faint and too close to the Sun in the sky to be seen. 2015 TB145 skypath

2018 flyby

After it had been unobservable for almost three years, was recovered on 7 October 2018 by L. Buzzi at Schiaparelli Observatory (

observatory code This is a list of observatory codes (IAU codes or MPC codes) published by the Minor Planet Center. For a detailed description, ''see observations of small Solar System bodies''. List References * {{DEFAULTSORT:Observat ...

204), at apparent magnitude 21. The 11 November 2018 flyby was about from Earth.

Observations

Radar imagery

The close approach was studied with

radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...

using Goldstone, the

Green Bank Telescope The Robert C. Byrd Green Bank Telescope (GBT) in Green Bank, West Virginia, US is the world's largest fully steerable radio telescope, surpassing the Effelsberg 100-m Radio Telescope in Germany. The Green Bank site was part of the National Radio ...

, and the

. It was one of the best radar targets of the year with a resolution as high as per pixel. Bistatic radar images created with the Green Bank Telescope had a resolution of per pixel. Arecibo images had a resolution of per pixel.

Possible cometary origin

The high

orbital inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth ...

and eccentricity suggest may be an

extinct comet An extinct comet is a comet that has expelled most of its volatile ice and has little left to form a tail and coma. In a dormant comet, rather than being depleted, any remaining volatile components have been sealed beneath an inactive surface la ...

that has shed its volatiles after numerous passes around the Sun. Orbital calculations by Petrus Jenniskens and Jérémie Vaubaillon showed that it was not expected to produce associated meteors in 2015. Any meteoroids were expected to pass more than from Earth's orbit. If meteoroids related to this asteroid were to cross Earth's path, the radiant is expected to be near Northern Eridanus. Cameras for Allsky Meteor Surveillance (CAMS) did not detect any activity in the presumed area of the sky during 2013 and 2014. The object has a low

albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...

of 0.06, which is only slightly more than a typical comet that has an albedo of 0.03-0.05.

Notes

References

External links

ALERT! Bright NEO 2015 TB145 on 29–31 October 2015
Ian Musgrave (itelescope)
WebCite archive of JPL solution #2 from 14 October 2015

Halloween Asteroid is a Radar Science Treat
(NASA Jet Propulsion Laboratory on YouTube)
Halloween Asteroid 2015 TB145 Flyby
Jerry Hilburn, 10/31/2015 12:12-12:24AM, Catfish Observatory, Teirra Del Sol, Canon 5D and an Orion ED 80 Refractor on an AVX Celestron Mount * * * {{DEFAULTSORT:2015 TB145 # Minor planet object articles (unnumbered) # Venus-crosser asteroids Mercury-crossing asteroids # # 20151031 20151010