Why Pluto is still a planet and hundreds more lurk in the Solar System

The chief scientist on NASA’s New Horizons mission has renewed his criticism of astronomers who voted to remove Pluto’s status as a planet.

Four images from New Horizons’ Long Range Reconnaissance Imager (LORRI) were combined with colour data from the Ralph instrument to create this enhanced color global view of Pluto. Image Credit: NASA/JHUAPL/SwRI

Dr Alan Stern holds the view that Pluto is still a planet, and that there must be hundreds more in the Sun’s family of worlds, rather than just eight.

But, talking exclusively to Skymania’s Paul Sutherland, he said that such a long list would not worry planetary scientists.

We spoke to Dr Stern, who has co-authored a new book called Chasing New Horizons, for a new podcast called the Sound of Astronomy which revives an audio magazine launched half a century ago.

Pluto, discovered in 1930, was demoted to the new status of dwarf planet by a gathering of the International Astronomical Union in August 2006. At the time, New Horizons was just six months into its nine-year journey to what had previously been regarded as the ninth planet.

Dr Stern told us: “It’s a completely illegitimate demotion by non-experts in the field, by astronomers rather than planetary scientists.

“Really, I think that the astronomers should stick to black holes and galaxies. They wouldn’t want us trying to classify those because we’re not experts. And in planetary science we consider — we broadly consider — Pluto and the small planets of the Kuiper Belt to be full-fledged planets, and we just kind of ignore what the astronomers do.

“It’s too bad that so much of the press gobble that down without any real critical thinking.”

With other icy worlds comparable to Pluto being discovered in the Kuiper Belt in the far reaches of the Solar System, we asked Dr Stern how many planets he thought there were.

He told us: “Well we now know of about 29 but we estimate that there are probably several hundred. So you know the Solar System was much better at making planets than anyone ever thought.

“And just like the fact that there are countless stars, countless galaxies, and for that matter countless mountains and rivers on the Earth, we’re not afraid of long lists of names. If the astronomers are, then that’s their problem!”

You can hear the full interview on the new edition of the Sound of Astronomy, a magazine-style show produced by leading organisation for beginners to stargazing, the Society for Popular Astronomy. Skymania contributor Osnat Katz is in charge of the revival.

And if you are interested in reading Chasing New Horizons, a fascinating account of the Pluto mission, for yourself, you can order a copy via this link.

The society was ahead of its time when it produced the first three issues of the Sound of Astronomy in the mid-Sixties, pre-dating the popular podcast format by more than 30 years, and before humans had even walked on the Moon.

The audio magazine was professionally put together in a TV studio in central London and mailed, on loan, to society members on reel-to-reel magnetic tape. Those early episodes have now been digitised and can be found at soundcloud.com/popastro.

An image from New Horizons of dunes on the shoreline of Sputnik Planum. Image credit: NASA/JHUAPL/SwRI

New Horizons, which is now heading for a Kuiper Belt object nicknamed Ultima Thule, zipped past Pluto at great speed in July 2015. But its brief encounter was a revelation, providing space scientists with a first close look at Pluto and data that will keep them busy for many years.

Only this week, the discovery of sand dunes on Pluto was announced – but these are formed from grains of methane ice that were released into its ultra-thin atmosphere.

The dunes can be seen pressed up against a major mountain range on the boundary of the Sputnik Planitia ice plain. Research led by scientists from the University of Plymouth in the UK, University of Cologne, Germany, and Brigham Young University, USA, is reported in the journal Science.

The video below shows how the process is believed to have created the dunes within the last 500,000 years.

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