is a sub-kilometer

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

, classified as

near-Earth object A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun ( perihelion) is less than 1.3 times the Earth–Sun distance (astronomical unit, AU). This definition applies to the object's orbit a ...

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 which is large enough to cause significant regional damage in the event of impact. Th ...

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. It is privately-owned by a consortium of investors including The Vistria Grou ...

, approximately in diameter. It safely passed 1.27

lunar distance The instantaneous Earth–Moon distance, or distance to the Moon, is the distance from the center of Earth to the center of the Moon. In contrast, the Lunar distance (LD or \Delta_), or Earth–Moon characteristic distance, is a unit of measure ...

s from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

on 31 October 2015 at 17:01

UTC Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communica ...

, 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 ...

at an apparent magnitude of 20 using a

Ritchey–Chrétien telescope A Ritchey–Chrétien telescope (RCT or simply RC) is a specialized variant of the Cassegrain telescope that has a hyperboloid, hyperbolic primary mirror and a hyperbolic secondary mirror designed to eliminate off-axis optical errors (Coma (optic ...

. 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. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

, 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 Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. From the perspe ...

. 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 geography of Halloween, observed in many countries on 31 October, the eve of the Western Christianity, Western Christian f ...

television special ''

It's the Great Pumpkin, Charlie Brown ''It's the Great Pumpkin, Charlie Brown'' is a 1966 American animated Halloween television special based on the comic strip ''Peanuts'' by Charles M. Schulz. The third ''Peanuts'' special, and the second holiday-themed special, to be created, i ...

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

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

-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 u ...

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 Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

and then passed from Earth. The last approach this close by an object with absolute magnitude 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 Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

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 m ...

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 by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...

. 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 ** Vṛṣabha, in vedic astrology * Taurus (constellation), one of the constellations of the zodiac * Taurus (mythology), one of two Greek mythological ch ...

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 M ...

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:Observato ...

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 system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

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 Rad ...

, 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 fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

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-crossing asteroids Mercury-crossing asteroids # # 20151031 20151010