Add dwarf planet Haumea to the list of solar system objects with rings

Why are we only just discovering that Haumea has a ring? Well for one, it’s extremely hard to see, by virtue of being quite far away and pretty small, as mentioned. Astronomers had to wait for the dwarf planet to pass by a bright star (relative to Earth) in order to observe how Haumea blocked out the light from the star in the background. This kind of observation — of watching one body pass in front of another, usually brighter body — is known as occultation in the astronomy world, and is a fairly common method of inferring the mass, atmospheric density, and shape of astronomical objects. Indeed, in hunting for extrasolar planets, occultation is one excellent means of observing if nearby stars harbor their own planets.

Multiple ground-based telescopes all across Europe observed how the light from the star was dimmed as Haumea passed in front of it. A telltale dip in light preceding and following the occultation, at the same distance, revealed that Haumea likely had a ring.

This puts Haumea in a class of its own in terms of astronomical bodies with rings. In our solar system, most of the ringed planets are gas giants, not rocky planets. Earth is thought to have briefly had a ring, after a collision with a Mars-sized body, although that ring is believed to have eventually coalesced into the Moon. But a ring around a dwarf planet?

“Until a few years ago we only knew of the existence of rings around the giant planets; then, recently, our team discovered that two small bodies situated between Jupiter and Neptune, belonging to a group called centaurs, have dense rings around them, which came as a big surprise,” said Pablo Santos-Sanz, a member of the research team, in a press release. “Now we have discovered that bodies even farther away than the centaurs, bigger and with very different general characteristics, can also have rings,” he added.

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