BellaOnline Forums Education Astronomy Pluto - it's a whole new story now

The IAU could have simply accepted that a planet (1) orbited the Sun, (2) wasn't a moon and (3) was massive enough to be essentially spherical.

But there was already a precedent for not doing this because the asteroids were considered a different class of object. Ceres and a number of others had been listed as planets for I forget how many years.

There had been questions about Pluto's status for a long time, but the discovery of the Kuiper Belt placed Pluto firmly as a Kuiper Belt object, as Ceres was an asteroid.

But it seems to me that Pluto and Ceres could be both planets and members of another class, so dwarf planets is an unnecessary confusion. In any case, it also seems to me that dwarf planets are a kind of planet - doesn't make sense to consider them otherwise. I mean dwarf varieties of plant are still plants, aren't they?

Here's a bit of history: Pluto Is a Dwarf Planet.

Scientists and non-scientists are very taken with Pluto's large heart-shaped feature, first snapped by New Horizons before the historic fly-by. A general list of names for features in the Plutonian system has gone to the International Astronomical Union (IAU), but, informally, the team is calling the heart-shaped region Tombaugh Regio after Pluto's discoverer Clyde Tombaugh.

In the center left of Tombaugh Regio there's an immense plain. (It's been given the informal name Sputnik Planum.) The Long Range Reconnaissance Imager has provided images of features as small as 1 km (half a mile). The surface is broken into irregular segments about 20 km (12 miles) across with narrow troughs ringing them.

The surface itself is of interest, but the most astonishing feature is the lack of impact craters. Astronomers date surfaces by the amount of cratering, the most heavily cratered being the oldest. This surface seems to be no more than 100 million years old. That sounds old to us, but in astronomical and geological terms, it's very young. (Jupiter's moon Ganymede has areas that may be as old as four billion years!) This means that some process is resurfacing it. Jupiter's icy moon Europa is resurfaced by internal heat generated by its gravitational interaction with Jupiter. But what is the heat source for Plutonian geology?

Some bright spark has taken some of the New Horizons fly-by images and animated them into a short video. The first part takes us over Pluto's mountains Norgay Montes. Norgay was Norgay Tensing who, with Edmund Hillary, were the first two humans on the summit of Everest. The second part shows Sputnik Planum. I wrote about that yesterday - here's your chance to have a look at this strange plain.

If Pluto is a dwarf planet, are the other bodies that are similar to Pluto also dwarf planets? I believe Charon is one, but I know there are other objects in the Kupier Belt that are Pluto's size and have similar behavior.

There are two other officially-designated dwarf planets in the Kuiper Belt, Haumea and Makemake. They're both smaller than Pluto.

Mike Brown, discoverer of Eris, has a table of Kuiper Belt Objects (KBOs) rated by how likely they are to qualify as dwarf planets. There are ten near certainties and thirteen highly likelies. And in 2010 Uruguyan astronomer Gonzalo Tancredi evaluated about four dozen promising KBOs. He thought that fifteen of them qualified as dwarf planets, and said another nine were possibles.

In his 2010 report to the IAU Tancredi recommended, cautiously, that the top three on the list be accepted and listed as dwarf planets. These are also Brown's top three – Quaoar, Sedna and Orcus. (Brown's team discovered all three.)

But no response from the IAU. After all the uproar of the 2006 decision they don't seem to be too bothered about following up with a practical response of identifying and listing dwarf planets.

Korie, a very interesting question about Charon. It's considered to be Pluto's moon, but . . . Actually, there are several buts.

Charon is small. (Remember Pluto itself is smaller than the Moon.) BUT it's half the size of Pluto. So, comparatively speaking, you might say it's the biggest Moon we know.

There's a technical reason for seeing Pluto and Charon as odd. A moon doesn't, strictly speaking, orbit a planet. They both orbit a gravitational midpoint between them called a barycenter. Where one body (the planet) is more massive than the other (a moon), that barycenter is inside the planet. So we say that moons orbit planets. BUT the Pluto-Charon barycenter is not inside Pluto, though it's much closer to Pluto than Charon.

Therefore some astronomers say that Pluto and Charon should be a double dwarf planet.

Annotated image of the southern region of Sputnik Planum

1. There are two mountains ranges, informally named for the first two men to climb Everest – Tensing Norgay and Edmund Hillary. Norgay Montes was discovered first. The new range is Hillary Montes. It rises about 1.6 km (a mile) from the plains, and is somewhat north of Norgay Montes.

2. Sputnik Planum is a plain about the size of Texas. I wrote something about it in the July 20 posting. You can see it (and Hillary Montes) in this video made from New Horizons close-approach images.

3. There appears to be widespread flow of nitrogen ice that looks like the movement of glaciers on Earth.

4. Bill McKinnon says: “In the southernmost region of the heart, adjacent to the dark equatorial region, it appears that ancient, heavily-cratered terrain has been invaded by much newer icy deposits.” In other words, more recent activity.

5. The large crater highlighted in the image is about 50 km (30 miles) wide, approximately the size of the greater Washington, DC area.

This is an enhanced color image of Pluto. If you were close to Pluto, it wouldn't look as it does in the picture. This image has been made by combining mages from LORRI (Long Range Reconnaissance Imager) with color data from the Ralph instrument. Ralph is an imager that can image color and use infrared spectroscopy. Enhancement is a useful technique because it emphasizes differences in composition and texture. (©NASA/SWRI/JHUAPL)

Pluto is a long way from the Sun. An artist's impression of Pluto's sky suggests it might look something like this. (Credit: ESO/L. Calçada) The haziness is Pluto's nitrogen atmosphere.

At that distance the Sun would appear about the size Jupiter does in Earthly skies at opposition. (That's when Jupiter is closest to us.) But despite looking small, the Sun is a star and it would still be very bright. Yes, around a thousand times dimmer than from Earth, but still around 300 times brighter than a full Moon from Earth. You'd need eye protection - as for a solar eclipse - to look at it.

Stuart Robbins, a research scientist at the Southwest Research Institute in Boulder, Colorado has made a video with images taken by New Horizons in January of the Pluto System. NASA released it the other day.

"Pluto flies in for its close-up on July 14; we then pass behind Pluto and see the atmosphere glow in sunlight before the sun passes behind Charon. The movie ends with New Horizons’ departure, looking back on each body as thin crescents."