Know more about the dwarf planet 'Snow White'

Recently, the finding of a new dwarf planet dubbed ‘Snow White’ was announced. It was actually earlier observed in 2007 and known as ‘2007 OR10’. It is a faraway object that orbits the sun every 548 years and moves on an extremely elliptical orbit, which takes it as far as 100 times the Earth-Sun distance. The Earth-Sun distance is about 150 million km and is referred to as one astronomical unit (AU). Pluto takes 248 years to orbit the Sun and is at a distance of 40 AU.

Although named Snow White, the new dwarf planet is reddish in appearance indicating, possibly, the presence of methane ice. It can perhaps be even darker. With astronomers obtaining a fresh insight into the size of the new dwarf planet, it now becomes the largest unnamed object in the solar system. It is found to be about 1,500 km in diameter, making it the third largest dwarf planet after Pluto and Eris. However, there is some uncertainty about Snow White’s newly determined size and it is said that there possibilities of it being larger than observed or even smaller. Hence, Mike Brown of the California Institute of Technology, who was a part of the team that discovered Snow White in 2007, suggests researchers to consider this fact before determining its place in the list of dwarf planets.

Delving into smaller planets
It may be recalled that in 2006, in a resolution of the International Astronomical Union (IAU) general assembly, Pluto was demoted from its status as a planet and dubbed a dwarf planet. Five other objects that have been classified as dwarf planets are Eris (earlier thought to have a diameter of 2,400 km, 5% larger than Pluto but now estimated to be smaller at 2,236 km); the asteroid Ceres, Makemake (at 1,430 km diameter) and Haumea (which has an oblong shape, with 1,900 km diameter).

Eris, discovered in January 2005, by a Mt Palomar team lead by Michael Brown, is at its furthest point in its orbit, 15 billion km from the Sun, three times farther than Neptune. Like Pluto, Eris is also an icy object that has a satellite, Dysnomia. Incidentally, it was the same team led by Michael who discovered Snow White. A moon orbiting Makemake at a distance of about 20,000 km from the dwarf planet has been recently discovered.

The New Horizons spacecraft has provided many surprise discoveries about Pluto and its satellites, water ice dominating many of their features. Solar wind particles are also diverted by Pluto, forming a shield and even a ‘Plutopause’ has been identified.

But what exactly is a dwarf planet? It is a small solar system object that is in direct orbit around the Sun and has sufficient mass to have contracted to a spherical shape but has not cleared its orbital zone of planetary debris or planetesimals. Pluto and Eris among others are also recognised as Kuiper belt objects (KBO). These can be seen in the Kuiper belt, which is a large wide ring of celestial bodies that is further than Neptune and orbits the Sun. They orbit close to the plane of the solar system in a region that extends from Neptune orbit 30 AU out to a distance of 60 AU. There are also Plutinos, which are literally little Plutos. These are members of the Kuiper belt with an average distance, like Pluto. Orbiting at such a distance, they orbit the Sun twice in the same period as it takes Neptune to orbit three times around the Sun.

About 1/4th of the KBOs are Plutinos. Plutinos may be debris from a collision of another KBO with Pluto which resulted in the formation of Pluto’s large moon, Charon. KBOs — which are in orbit around the Sun, but are not held in orbital resonance with Neptune (unlike Plutinos) or any other planet — are dubbed as Cubewanos. This name originates from QB-1, the first known KBO that was discovered in 1992. It orbits the Sun between 40 and 50 AU).

Like Pluto and its moon, Snow White could also be composed of a mixture of ices with water ice dominating. This seems to be a feature of objects in the far reaches of the solar system.

The recent Juno
mission has a main goal of measuring the water ice content of Jupiter atmosphere. The amount of water could indicate whether Jupiter was formed in the inner solar system and then migrated outwards.

There could be several such icy dwarf planets and their moons in the outer solar system. The presence of vast quantities of water ice could make them potential candidates for life. Hardly two decades ago, nobody would have imagined that there could be thousands of objects beyond Neptune and Pluto. As our solar system continues expanding, our astronomy textbooks might have to be rewritten.