MIKE BROWN

The Guy Who Helped Demote Pluto

There’s a planetary scientist who cheerfully claims to have killed Pluto. His name is Mike Brown (1965–), member of a team that has discovered more outer solar system worlds than anyone else. In his defense, he claims that the distant little world deserved its fate. He even wrote a book about the subject, How I Killed Pluto and Why It Had It Coming, in which he explains the reasons why Pluto was demoted to dwarf planet status in 2006.

The Pluto-Killer Himself

Mike Brown is a professor of planetary science at the California Institute of Technology (CalTech). He was born and raised in Huntsville, Alabama, and went to college at Princeton and the University of California at Berkeley before moving to CalTech. His work in solar system exploration has netted him many awards, including Time magazine’s 100 Most Influential People, but on his web page, he notes that the most important honor for him was winning an honorable mention in his fifth-grade science fair. He and his family were greatly amused when Wired Online voted him one of the Top Ten Sexiest Geeks in 2006.

Mike Brown and his team of world-hunters are painstakingly searching out tiny places in the outer solar system called Trans-Neptunian Objects (TNO). These lie out past the orbit of Neptune. They include:

Eris is actually larger than Pluto, and it’s the world that started the whole “Pluto Is a Planet/No, It’s Not” controversy that led to that world’s redesignation as a dwarf planet.

Finding the Pluto-Killing World

Mike Brown, Chad Trujillo, and David Rabinowitz make up the TNO-hunting team that discovered Eris. They imaged it in 2003 during a sky survey as part of their systematic search for outer solar system bodies using the Samuel Oschin 1.2-meter telescope at the Palomar Observatory in southern California. Eris didn’t get flagged at that time because it wasn’t moving fast enough to be noticed as a potential TNO. Ultimately it turned up when the team analyzed their data. They did follow-up observations to calculate the object’s orbit and figure its distance. When the team was sure of its discovery, they announced it on July 29, 2005, about the same time as they revealed two other worlds (Haumea and Makemake).

It took so long to find Eris because it moves very slowly across the backdrop of the sky. Data analysis and further observations revealed that not only is Eris larger than Pluto, but it also has its own moon, now known as Dysnomia. The world is named after the Greek goddess of discord and strife, which is perfectly appropriate, given the great controversy that arose as astronomers decided that Pluto was no longer a planet and would, along with Eris, henceforth be classified as a dwarf plant.

About Eris

What do we know about this world that helped kill off Pluto’s planetary status? Eris appeared to be larger than Pluto when it was discovered, and people called it the “Tenth Planet” for a while. That nickname spurred discussion of just how many planets are out there, which then raised the question, “Well, what’s a planet?” That’s how the whole Pluto reclassification thing got started. Eris is also called a plutoid, which is another way to describe a TNO that’s a dwarf planet. Its diameter, as measured by the Hubble Space Telescope, and by a ground-based observation from LaSilla in Chile, is about 2,300 kilometers, which makes it about the same size as Pluto. Like other objects in the Kuiper Belt, Eris is probably made of half ice and half rock inside, with a surface covered largely by nitrogen ice with a smaller amount of methane ice. That’s a lot like Pluto!

Hunting for planets in the outer solar system is not an easy task. Clyde Tombaugh found that out in 1930 when he set about trying to find Planet X (later named Pluto). Objects in the outer solar system are dim and small, and because they orbit so far from the Sun, their orbits are very large. This means that they don’t move very quickly. Tombaugh had to examine many photographic plates, comparing them to each other, before he could detect Pluto’s plodding motion across the sky.

The same is true of today’s modern TNO-hunters. They must take painstaking survey observations over many nights to catch a glimpse of a dim and distant object. The farther away the objects are, the harder it is to detect their motion. Moreover, the surfaces of these objects are not very bright, which makes them harder to spot. Luckily, these searches can now be automated. For example, the Samuel Oschin Telescope can operate in what’s called a point-and-track mode, in which it locks onto a specific area of the sky and takes an exposure. Then it looks at other areas of the sky and takes a pre-set number of images before returning to the original area. If anything has moved in any of the views, it gets tagged for further review. This works really well in the search for dim, distant solar system objects such as comets and asteroids, as well as TNOs and objects out in the Kuiper Belt region beyond Neptune.

More New Worlds

Haumea and Makemake, the two worlds announced at about the same time as Eris, are also orbiting the Sun out beyond Neptune.

  1. Haumea is an ice-covered rocky body and is named after the goddess of the Big Island of Hawaii. It has two moons called Hi’aka and Namaka. This little world is oblong-shaped, somewhere around 2,500 kilometers long and about 1,500 kilometers across. It lies at a distance of 35 AU, and its orbit is 283 Earth years long.
  2. Makemake is an ice-covered dwarf planet with dimensions of about 1,500 kilometers by around 1,400 kilometers. At the most distant point of its orbit, it lies 53 AU from the Sun and takes nearly 310 Earth years to make one orbit.