From discovery to demotion: How a dwarf planet changed astronomy
Astronomer Mike Brown awoke one morning in 2005 and once again checked his computer for updates, as he had done for the last seven years. He scanned through about 200 images, discarding most. Each spot was either too slow, too dim, or just a satellite or other object orbiting the Earth. One image of the night sky, however, caught his eye. A single light stood brighter than the others. The following pictures revealed a slight movement. “Oh, God,” Brown thought. “We must have screwed up. It’s too bright. It’s too big. It’s too far away.”
Had he pointed the telescope at the wrong position in the sky, or accidentally seen an asteroid, or taken fast pictures? A minute or two of cross-checks verified the pictures were indeed accurate. The object glowed brighter than anything Brown and his team at Caltech's Palomar Observatory had ever discovered. The apparent slowness meant it was far from Earth. He ran a quick calculation: as big as Pluto, if not larger.
“It was obvious within the first 10 seconds that this changed everything,” Brown said. He phoned his wife and told her the news: He had just discovered an object big enough to be the solar system’s tenth planet.
Brown and his co-discoverers nicknamed their discovery Xena, after the '90s TV icon. But after realizing the impact it would have on the scientific community, the team officially named the object for the Greek goddess of discord and strife, Eris.
Meanwhile, a NASA mission called New Horizons was in the final stages before launch. In a few months it would send a spacecraft on a 10-year journey to Pluto, in a region never closely explored before. The discovery of Eris would have ripple effects on the mission and its lead scientist, who suddenly found himself at the heart of an international controversy that rattled the foundations of one of mankind’s oldest sciences.
A solar system unraveling
At the time of the Eris discovery, our knowledge of the solar system’s planets was fairly robust. Unmanned probes had visited the gas giants (Jupiter, Saturn, Uranus and Neptune) in the 1980s with subsequent missions to Jupiter and Saturn. Several missions surveyed the inner planets of Venus and Mars over the years. And while our innermost planet, Mercury, had only been partially explored, our outermost planet, Pluto, and the region beyond Neptune, had never been visited and remained mysterious.
It was the introduction of a class of highly sensitive detectors that would shed light on Pluto and revolutionize the field, ushering in a new era for astronomy. The technology applied charged coupled devices (CCDs), which are often found in digital cameras today, to a technique called drift scanning to track movement in the sky down to individual photons. This allowed astronomers to gaze beyond Neptune to a zone they soon realized was clustered with large, icy objects left over from the formation of the solar system. It became defined as the Kuiper Belt.
By 2001 several teams, such as the Deep Eliptical Survey, the Outer Solar System Survey, and the Lincoln Near-Earth Asteroid Research (LINEAR) project, were combing the Kuiper Belt for bright objects, with high success rates.
“We suddenly had the capabilities of surveying the whole sky. We found pretty much everything there was to find that was as bright as Eris,” Brown said. “So it wasn’t just Eris. It was the discovery of Eris and the other big dwarf planets, Quaoar (in 2002), Haumea (in 2004), Orcus (in 2004) and Makemake (in 2005).
“Each of these little objects holds a tiny bit of the claim to the history of the solar system. And each one is different. Each one had this story that we had to learn how to read,” he said. “And we were starting to figure out these stories for the first time ever. No one had ever found these objects. No one knew anything about them. That’s the part that I think, looking back, will be the highlight of my career.”
If these contributions to astronomy were astounding, their impacts on the status of the ninth planet were profound. Brown, who studied Eris with his team for two years before announcing their findings to the world, knew the discovery would lead to one of two options: Either Eris would be classified as the tenth planet or Pluto would be downgraded to the dwarf planet subclass.