It was discovered in November 2000 by American astronomer Robert McMillan during a Spacewatch survey at the Kitt Peak National Observatory.

Varuna's light curve is compatible with the body being a Jacobi ellipsoid, suggesting that it has an elongated shape due to its rapid rotation.

Water ice is also present on its surface, and is thought to have been exposed by past collisions which may have also caused Varuna's rapid rotation.

Varuna was discovered by American astronomer Robert McMillan using the Spacewatch 0.9-meter telescope during a routine survey on 28 November 2000.

[1] At the time of discovery, Varuna was located at a moderately dense star field close to the northern galactic equator.

[1] These precovery images along with additional observations from Japan, Hawaii, and Arizona helped astronomers refine its orbit and determine Varuna's proper classification.

CCD photometry of Varuna's light curve in 2001 revealed that it displays large brightness variations with an amplitude of about 0.5 magnitudes.

[9] This increase in amplitude is due to the combined effects of Varuna's ellipsoidal shape, rotation, and varying phase angle.

[42] Due to Varuna's ellipsoidal shape, multiple observations have provided different estimates for its diameter, ranging from 500–1,000 km (310–620 mi).

[41] An occultation by Varuna in February 2010 yielded a chord length of 1,003 km (623 mi), inferred to be across its longest axis.

[42] Astronomer William Grundy and colleagues propose that dark, low-density TNOs around the size range of approximately 400–1,000 km (250–620 mi) are likely to be uncompressed, partially porous bodies.

While the larger objects in this range, such as Varuna, may have fully collapsed into solid material in their interiors, their surfaces likely remain uncompressed.

[43] Contrary to the ground-based estimates, space-based thermal observations from the Spitzer Space Telescope provided a smaller diameter range of 450–750 km (280–470 mi).

[50] Distant trans-Neptunian objects such as Varuna intrinsically emit thermal radiation at longer wavelengths due to their low temperatures.

[51][52] In 2010, an occultation by Varuna was successfully observed by a team of astronomers led by Bruno Sicardy on the night of 19 February.

The occultation yielded a chord length of 1003±9 km, quite large compared to mean diameter estimates from thermal measurements.

Varuna's spectrum was first analyzed in early 2001 with the Near Infrared Camera Spectrometer (NICS) at the Galileo National Telescope in Spain.

Varuna's spectrum also exhibits strong absorption bands at wavelengths of 1.5 and 2 μm, indicating the presence of water ice on its surface.

[56][31] The red color of Varuna's surface results from the photolysis of organic compounds being irradiated by sunlight and cosmic rays.

[56] Another study of Varuna's spectra at near-infrared wavelengths in 2008 yielded a featureless spectrum with a blue spectral slope, contrary to earlier results in 2001.

[58] Additional near-infrared observations of Varuna's spectra were conducted at the NASA Infrared Telescope Facility in 2017 and have identified absorption features between 2.2 and 2.5 μm that might be associated with ethane and ethylene, based on preliminary analysis.

[8] Varuna is among the twenty brightest trans-Neptunian objects known, despite the Minor Planet Center assuming an absolute magnitude of 3.6.

The photometry results also showed an increase in asymmetry of Varuna's light curve near opposition, indicating variations of scattering properties over its surface.

[42] Varuna's low bulk density is likely due to a porous internal structure composed of a nearly proportional ratio of water ice and rock.

Varuna's granular internal structure is thought to have resulted from fractures caused by past collisions likely responsible for its rapid rotation.

[20] Other objects including Saturn's moons Tethys and Iapetus are also known to have a similarly low density, with a porous internal structure and a composition that is predominantly water ice and rock.

[20] William Grundy and colleagues proposed that dark, low-density TNOs around the size range of approximately 400–1,000 km (250–620 mi) are transitional between smaller, porous (and thus low-density) bodies and larger, denser, brighter and geologically differentiated planetary bodies (such as dwarf planets).

[49] The internal structures of low-density TNOs, such as Varuna, had only partially differentiated, as their likely rocky interiors had not reached sufficient temperatures to melt and collapse into pore spaces since formation.

They plotted the residuals of the combined light curve in a Lomb periodogram and derived an orbital period of 11.9819 hours for the possible satellite.

[9] Planetary scientist Amanda Zangari calculated that a flyby mission to Varuna could take just over 12 years using a Jupiter gravity assist, based on a launch date of 2035 or 2038.