Near-Earth asteroid in the context of "2021 PH27"

A formal minor-planet designation is, in its final form, a number–name combination given to a minor planet (asteroid, centaur, trans-Neptunian object and dwarf planet but not comet). Such designation always features a leading number (catalog or IAU number) assigned to a body once its orbital path is sufficiently secured (so-called "numbering"). The formal designation is based on the minor planet's provisional designation, which was previously assigned automatically when it had been observed for the first time. Later on, the provisional part of the formal designation may be replaced with a name (so-called "naming"). Both formal and provisional designations are overseen by the Minor Planet Center (MPC), a branch of the International Astronomical Union.

Currently, a number is assigned only after the orbit has been secured by four well-observed oppositions. For unusual objects, such as near-Earth asteroids, numbering might already occur after three, maybe even only two, oppositions. Among more than half a million minor planets that received a number, only about 20 thousand (or 4%) have received a name. In addition, approximately 700,000 minor planets have not been numbered, as of November 2023.

The following is a list of Solar System objects by orbit, ordered by increasing distance from the Sun. Most named objects in this list have a diameter of 500 km or more.

• The Sun, a spectral class G2V main-sequence star
• The inner Solar System and the terrestrial planets
  • Mercury
    • Mercury-crossing minor planets
  • Venus
    • Venus-crossing minor planets
      • Zoozve, Venus' quasi-satellite
  • Earth
    • Moon
    • Near-Earth asteroids
      • 2021 PH27
      • Apophis
      • Eros
    • Earth trojans (2010 TK7)
    • Earth-crosser asteroids
      • Earth's quasi-satellites
  • Mars
    • Deimos
    • Phobos
    • Mars trojans
    • Mars-crossing minor planets
  • Asteroids in the asteroid belt, between the orbits of Mars and Jupiter
    • Ceres, a dwarf planet
    • Vesta
    • Pallas
    • Hygiea
    • Europa (asteroid)
    • Davida
    • Sylvia
    • Asteroids number in the hundreds of thousands. For longer lists, see list of exceptional asteroids, list of asteroids, or list of Solar System objects by size.
      • Asteroid moons
  • A number of smaller groups distinct from the asteroid belt
• The outer Solar System with the giant planets, their satellites, trojan asteroids and some minor planets
  • Jupiter
    • Rings of Jupiter
    • Complete list of Jupiter's natural satellites
      • Galilean moons
        • Io
        • Europa (moon)
        • Ganymede
        • Callisto
    • Jupiter trojans
    • Jupiter-crossing minor planets
  • Saturn
    • Rings of Saturn
    • Complete list of Saturn's natural satellites
      • Mimas
      • Enceladus
      • Tethys (trojans: Telesto and Calypso)
      • Dione (trojans: Helene and Polydeuces)
      • Rhea
        • Rings of Rhea (largely disproven)
      • Titan
      • Hyperion
      • Iapetus
      • Phoebe
      • Shepherd moons
    • Saturn-crossing minor planets
  • Uranus
    • Rings of Uranus
    • Complete list of Uranus's natural satellites
      • Miranda
      • Ariel
      • Umbriel
      • Titania
      • Oberon
    • Uranus trojan (2011 QF99)
    • Uranus-crossing minor planets
  • Neptune
    • Rings of Neptune
    • Complete list of Neptune's natural satellites
      • Proteus
      • Triton
      • Nereid
    • Neptune trojans
    • Neptune-crossing minor planets
  • Non-trojan minor planets
    • Centaurs
      • Chiron
      • Chariklo
    • Damocloids
  • Trans-Neptunian objects (beyond the orbit of Neptune)
    • Kuiper-belt objects (KBOs)
      • Plutinos
        • Orcus, a dwarf planet
          • Vanth
        • Pluto, a dwarf planet
          • Complete list of Pluto's natural satellites
            • Charon
        • Ixion
        • Achlys
      • Twotinos
      • Cubewanos (classical objects)
        • Haumea, a dwarf planet
          • Namaka
          • Hiʻiaka
        • Quaoar, a dwarf planet
          • Weywot
        • Makemake, a dwarf planet
          • S/2015 (136472) 1
        • Máni
        • Salacia
          • Actaea
        • Aya
        • Varda
          • Ilmarë
        • Varuna
        • Ritona
        • Arrokoth
    • Scattered-disc objects
      • Gonggong, a dwarf planet
        • Xiangliu
      • Eris, a dwarf planet
        • Dysnomia
      • Chiminigagua
      • (84522) 2002 TC302
      • (87269) 2000 OO67
      • 2015 TH367/V774104
    • Detached objects
      • (612911) 2004 XR190
      • 2012 VP113 (possibly inner Oort cloud)
      • Sedna, a dwarf planet (possibly inner Oort cloud)
    • Oort cloud (hypothetical)
      • Hills cloud/inner Oort cloud
      • Outer Oort cloud

The Chelyabinsk meteor (Russian: Челябинский метеорит, romanised: Chelyabinskiy meteorit) was a superbolide that entered Earth's atmosphere over the southern Ural region in Russia on 15 February 2013 at about 09:20 YEKT (03:20 UTC). It was caused by an approximately 18-meter (60 ft), 9,100-tonne (10,000-short-ton) near-Earth asteroid that entered the atmosphere at a shallow 18‐degree angle with a speed relative to Earth of about 19.2 km/s (68,980 km/h; 42,860 mph). The light from the meteor was briefly brighter than the Sun (which is about -26.7 magnitude), visible as far as 100 kilometers (62 miles) away. It was observed in a wide area of the region and in neighbouring republics. Some eyewitnesses also reported feeling intense heat from the fireball.

The object exploded in a meteor air burst over Chelyabinsk Oblast, at a height of about 30 kilometres (18.6 miles). The explosion generated a bright flash, producing a hot cloud of dust and gas that penetrated to 26 kilometres (16 mi), and many surviving small fragmentary meteorites. Most of the object's energy was absorbed by the atmosphere, creating a large shock wave. The asteroid had a total kinetic energy before atmospheric impact equivalent to the blast yield of 400–500 kilotonnes of TNT (1.7–2.1 petajoules), estimated from infrasound and seismic measurements. This was approximately 30 times as much energy as that released by the atomic bomb detonated at Hiroshima.

2017 YE₅ is a binary pair of asteroids of approximately equal size and mass, each about 0.9 km (0.56 mi) in diameter. Classified as a near-Earth asteroid and potentially hazardous object of the Apollo group, 2017 YE₅ was discovered by amateur astronomer Claudine Rinner at the Oukaïmeden Observatory on 21 December 2017. On 21 June 2018, the pair of asteroids passed within 15.5 lunar distances or approximately 6 million km (3.7 million mi) from Earth. During the close encounter, 2017 YE₅ was resolved in high detail by concurrent radar observations by the Arecibo and Green Bank observatories, along with individual observations by the Goldstone Solar System Radar. 2017 YE₅ is likely an extinct or dormant comet due to its distant elliptical orbit and dark red surface.

The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, discovered by German astronomer Karl Reinmuth in the 1930s. They are Earth-crossing asteroids that have an orbital semi-major axis greater than that of the Earth (a > 1 AU) but perihelion distances less than the Earth's aphelion distance (q < 1.017 AU).

As of January 2025, the number of known Apollo asteroids is 21,083, making the class the largest group of near-Earth objects (cf. the Aten, Amor and Atira asteroids), of which 1,742 are numbered (asteroids are not numbered until they have been observed at two or more oppositions), 81 are named, and 2,130 are identified as potentially hazardous asteroids.

The Amor asteroids are a group of near-Earth asteroids named after the archetype object 1221 Amor /ˈeɪmɔːr/. The orbital perihelion of these objects is close to, but greater than, the orbital aphelion of Earth (i.e., the objects do not cross Earth's orbit), with most Amors crossing the orbit of Mars. The Amor asteroid 433 Eros was the first asteroid to be orbited and landed upon by a robotic space probe (NEAR Shoemaker).

The uncertainty parameter U is introduced by the Minor Planet Center (MPC) to quantify the uncertainty of a perturbed orbital solution for a minor planet. The parameter is a logarithmic scale from 0 to 9 that measures the anticipated longitudinal uncertainty in the minor planet's mean anomaly after 10 years. The larger the number, the larger the uncertainty. The uncertainty parameter is also known as condition code in JPL's Small-Body Database Browser. The U value should not be used as a predictor for the uncertainty in the future motion of near-Earth objects.

Near Earth Asteroid Rendezvous – Shoemaker (NEAR Shoemaker), renamed after its 1996 launch in honor of planetary scientist Eugene Shoemaker, was a robotic space probe designed by the Johns Hopkins University Applied Physics Laboratory for NASA to study the near-Earth asteroid Eros from close orbit over a period of a year. It was the first spacecraft to orbit an asteroid and land on it successfully. In February 2000, the mission closed in on the asteroid and orbited it. On February 12, 2001, Shoemaker touched down on the asteroid and was terminated just over two weeks later.

The primary scientific objective of NEAR was to return data on the bulk properties, composition, mineralogy, morphology, internal mass distribution, and magnetic field of Eros. Secondary objectives include studies of regolith properties, interactions with the solar wind, possible current activity as indicated by dust or gas, and the asteroid spin state. This data was used to help understand the characteristics of asteroids in general, their relationship to meteoroids and comets, and the conditions in the early Solar System. To accomplish these goals, the spacecraft was equipped with an X-ray/gamma-ray spectrometer, a near-infrared imaging spectrograph, a multi-spectral camera fitted with a CCD imaging detector, a laser rangefinder, and a magnetometer. A radio science experiment was also performed using the NEAR tracking system to estimate the gravity field of the asteroid. The total mass of the instruments was 56 kg (123 lb), requiring 80 watts of power.

Clementine (officially called the Deep Space Program Science Experiment (DSPSE)) was a joint space project between the Ballistic Missile Defense Organization (previously the Strategic Defense Initiative Organization) and NASA, launched on January 25, 1994. Its objective was to test sensors and spacecraft components in long-term exposure to space and to make scientific observations of both the Moon and the near-Earth asteroid 1620 Geographos.

Its lunar observations included imaging at various wavelengths in the visible as well as in ultraviolet and infrared, laser ranging altimetry, gravimetry, and charged particle measurements. These observations were for the purposes of obtaining multi-spectral imaging of the entire lunar surface, assessing the surface mineralogy of the Moon, obtaining altimetry from 60°N to 60°S latitude, and obtaining gravity data for the near side. There were also plans to image and determine the size, shape, rotational characteristics, surface properties, and cratering statistics of Geographos. However, observation of the asteroid was not made due to a malfunction in the spacecraft.

(706765) 2010 TK₇ (provisional designation 2010 TK₇) is a sub-kilometer Near-Earth asteroid and the first Earth trojan discovered; it precedes Earth in its orbit around the Sun. Trojan objects are most easily conceived as orbiting at a Lagrangian point, a dynamically stable location (where the combined gravitational force acts through the Sun's and Earth's barycenter) 60 degrees ahead of or behind a massive orbiting body, in a type of 1:1 orbital resonance. In reality, they oscillate around such a point. Such objects had previously been observed in the orbits of Mars, Jupiter, Neptune, and the Saturnian moons Tethys and Dione.

2010 TK₇ has a diameter of about 300 meters (1,000 ft). Its path oscillates about the Sun–Earth L₄ Lagrangian point (60 degrees ahead of Earth), shuttling between its closest approach to Earth and its closest approach to the L₃ point (180 degrees from Earth).

An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earth's orbit. The known numbered Earth-crossers are listed here. Those Earth-crossers whose semi-major axes are smaller than Earth's are Aten asteroids; the remaining ones are Apollo asteroids. (See also the Amor asteroids.)

An asteroid with an Earth-crossing orbit is not necessarily in danger of colliding with Earth. The orbit of an Earth-crossing asteroid may not even intersect with that of Earth. This apparent contradiction arises because many asteroids have highly inclined orbits, so although they may have a perihelion less than that of Earth, their paths can never cross. An asteroid for which there is some possibility of a collision with Earth at a future date and which is above a certain size is classified as a potentially hazardous asteroid (PHA). Specifically, an asteroid is a PHA if its Earth minimum orbital intersection distance (MOID) is <0.05 AU and its absolute magnitude is 22 or brighter. The concept of PHA is intended to replace the now abandoned strict definition of ECA (Earth-crossing asteroid) which existed for a few years. Determining if an asteroid was an ECA required calculation of its orbits millennia into the future, including planetary gravitational perturbations, to assess whether a collision with Earth was possible and this has proved to be impractical.