| Minorplanet: | yes |
| 4034 Vishnu | |
| Background: |
|
| Discovery Ref: |   |
| Discovered: | 2 August 1986 |
| Mpc Name: | (4034) Vishnu |
| Alt Names: | 1986 PA |
| Orbit Ref: |   |
| Epoch: | 6 January 2010 (JD 2455202.5) |
| Uncertainty: | 0 |
| Observation Arc: | 28.93 yr (10,565 days) |
| Perihelion: | 0.5891 AU |
| Semimajor: | 1.0595 AU |
| Eccentricity: | 0.4439 |
| Period: | 1.09 yr (398 days) |
| Mean Motion: | / day |
| Inclination: | 11.170° |
| Asc Node: | 158.01° |
| Arg Peri: | 296.60° |
| Albedo: | 0.52 |
| Spectral Type: | SMASS O  |
| Abs Magnitude: | 18.4 |
4034 Vishnu (prov. designation:) is a rare-type asteroid classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 420m (1,380feet) in diameter. It was discovered on 2 August 1986, by American astronomer Eleanor Helin at Palomar Observatory in California, United States. It is named after the Hindu deity Vishnu.
This minor planet was named for the four-armed god of protection and preservation of good, Vishnu, one of the principal deities of Hinduism. The asteroid's name was proposed by Belgian amateur astronomer and professional meteorologist Jean Meeus. The approved naming citation was published by the Minor Planet Center on 15 July 2011 .
Vishnu orbits the Sun at a distance of 0.6–1.5 AU once every 1 years and 1 month (398 days). Its orbit has an eccentricity of 0.44 and an inclination of 11° with respect to the ecliptic. As no precoveries were taken, and no prior identifications were made, the body's observation arc begins with its official discovery observation at Palomar in 1986.
Vishnu is a potentially hazardous asteroid due to its sufficiently large size and low Earth minimum orbital intersection distance of 0.0194AU, which corresponds to 7.6 lunar distances.
Its highly eccentric orbit crosses the orbits of all inner planets except that of Mercury, which effectively makes it a Venus-crosser, Earth-crosser and Mars-crosser all at once. From 1800 to 2200, Vishnu has made and will make multiple approaches of Venus (71×), Earth (29×), and Mars (7×) within 30 gigameters. It has been observed by radar astronomy (Binzel) and the orbital solution includes non-gravitational forces.
In the SMASS taxonomy, Vishnu is a rare O-type asteroid, meaning it is similar to the asteroid 3628 Boznemcová, which is the best asteroid match to the spectra of L6 and LL6 ordinary chondrite meteorites. These L and LL chondrites have lower iron metal content, but higher iron oxide content in the silicates.
In the early 2000s, Vishnu has been observed in the thermal-infrared by the Keck telescope on Mauna Kea, Hawaii. The asteroid measures approximately 420 meters in diameter and its surface has a high albedo of 0.520. As of 2017, Vishnu rotation period and shape remain unknown as no lightcurves have yet been obtained.