Category Archives: Pluto

dwarf planets, planets, Pluto

Pluto’s New Moon

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A Dwarf Planet with Moons

Pluto has been in the news a lot lately. The New Horizons spacecraft is headed out to swoop past this icy dwarf planet and show us what it really looks like.  That will happen in July 2015 — just three years from now.  In the meantime, the Hubble Space Telescope keeps checking out this distant world and finding new moons around it. The HST observations are an ongoing project to make sure that mission planners for New Horizons have a good idea of the known hazards (i.e. things that the spacecraft could hit) as it whizzes past Pluto in a few years.

The dwarf planet Pluto and its five moons. Will HST find more? Courtesy NASA/STScI.

Last week, the HST folks announced the discovery of a fifth moon orbiting Pluto. For now, it’s called P5, and in time, it will get an official name.

Pluto’s moons, with the exception of its largest moon Charon, are pretty small. This newly discovered one is no bigger than 15 miles across.  Now, it’s kind of intriguing that Pluto has so many of its own moons, and scientists are busily figuring out how it could have gained such a following through its history. The current thinking is that these little moons  are debris from a collision between Pluto and another object early in the history of the solar system, and subsequently were swept into Pluto’s orbit.

Collisions ARE an important part of solar system evolution. Earth’s own Moon was most likely formed in the aftermath of a collision between the infant Earth and a Mars-sized object.  And, we still see collisions today: comets collide with planets, asteroids collide, objects in Saturn’s rings collide, and so on. Collisions are a fact of life when you live in a planetary system and people in planetary science are still defining and understanding the role that smashups play in the larger evolution of worlds.

The New Horizons mission is a small spacecraft that proposed to NASA after the Pluto Kuiper Express mission got cancelled by the agency due to lack of funds. New Horizons has moved out beyond the orbit of Uranus, carrying a suite of scientific instruments, including a set of cameras, radio science detectors, plasma and high-energy particle detectors, and a dust counter. It has already sent back data and images  Jupiter and some of its moons, and an asteroid.

Once the mission gets to Pluto, it will fly quite close to this frozen world and take massive amounts of data about its surface and atmosphere.  After that, the spacecraft heads out to explore more of the Kuiper Belt and relay information about this unexplored frontier of the solar system. Stay tuned!

 

clyde tombaugh, dwarf planets, planets, Pluto

It Was 82 Years Ago

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The Rise of the Dwarf Planets

A Hubble Space Telescope image of Pluto (central object) and its four largest moons, Hydra (upper left), Charon (lower left), Nix (lower right), and P4 (upper right). Courtesy NASA/ESA/STScI.

February 18th is the 82nd anniversary of the discovery of Pluto, the dwarf planet.  The find was made in 1930 by an observer at Lowell Observatory in Arizona by the name of Clyde Tombaugh.  He had spent months searching through and comparing photographic plates of the sky, looking for a possible new planet. His discovery was confirmed, and the name Pluto was bestowed on March 24, 1930.  I had the pleasure to meet Clyde at a conference some years ago, when he spoke enthusiastically about his work to uncover this distant, frozen world.

Pluto is classified as a dwarf planet — which means it’s a special class of planet, much as white dwarfs are special classes of stars, and some galaxies are termed “dwarfs” based on the characteristics that differentiate them from spiral, elliptical, and irregular galaxies.

One of the fascinating things (among many) about Pluto is that its discovery really opened up a new phase of solar system exploration, resulting the discovery of more dwarf planets  in the outer solar system.

Granted, we’ve done quite a bit of solar system exploration since Clyde’s momentous discovery.  We’ve sent probes to most of the other planets, and studied them with ground- and space-based telescopes.  But, until recently, we didn’t have the technical wherewithal to do more than study Pluto from Earth (or Earth orbit, with Hubble Space Telescope, for example).  That changed when the New Horizons spacecraft was launched in 2006 on an voyage of exploration of the outer solar system.

New Horizons will arrive at Pluto in 2015.  It will study the planet’s atmosphere, surface characteristics, and its nearest moons.  After that, it will continue out to other outer solar system objects — in fact, its larger mission is to study the Kuiper Belt, a region of space that extends out from the orbit of Neptune and in which Pluto orbits .  It’s really the gateway to all the outer solar system worlds, including Pluto.

I mentioned that astronomers have found other icy worlds out in Pluto’s domain, and beyond. Eris is the most massive known dwarf planet (so far), and orbits the Sun out well beyond Pluto.  It’s an icy world roughly the size of Plut0. Then, there are Makemake, Haumea, Charon, Orcus, Quaoar, and Sedna.  They’re all smaller and more distant than Pluto, but there’s no doubt they’re worlds in their own right. Undoubtedly others are out there, making trans-Neptunian space a sort of new frontier.  This is why I see Pluto’s discovery as momentous. So, in celebration of Pluto Discovery Day, I raise a toast to Clyde Tombaugh — whose ashes are aboard the New Horizon spacecraft bound for Pluto space.  Not only did he discover a dwarf planet, but he also opened the gates to discoveries in a sector of the solar system once thought empty and barren.  It’s a bigger solar system than we thought, folks, and we have visionaries like Clyde to thank for helping us figure that out.