23Aug2015

It’s Time To Make Pluto A Proper Planet Again

Neil deGrasse Tyson

Pluto hater … Your arse is DeGrasse, Tyson

Those who feel that Pluto has always been a planet and jolly well ought to be one again have received a boost – this time from a top NASA boffin, albeit a slightly biased one.

“It’s very hard not to call an object with this level of complexity in its geology, and such complex seasons, a planet,” said Alan Stern, New Horizons’ principal investigator at Southwest Research Institute, during a press conference about the probe’s latest update.

A Joint Decision

“Astronomers and planetary scientists differ on this question but that’s how science works – scientists make individual decisions and consensus is reached. I think we’re going through a period of transition at the moment.”

Data from the New Horizons space probe has shown Pluto to be geologically active, with new glacier plains of nitrogen ice carving out new surface features and eroding away impact craters from meteor strikes.

It has a large, hazy atmosphere extending 100 miles from the surface, and the New Horizons data has revealed a lot about the dwarf planet’s history. We heard during the briefing that Pluto is almost perfectly spherical, which was unexpected considering what we think happened during its formation.

Past History Hints

It’s likely that way back in its history, Pluto was hit by a massive object that tore away a huge chunk of its mass, which went on to form into the freezeworld’s five moons.

But no remnant of that impact can be seen on the surface or in its current clean, spherical form.

That means that Pluto must have been spinning very rapidly after the impact, William McKinnon, New Horizons co-investigator at Washington University said, before reaching equilibrium with its relatively massive moon Charon.

The case against Pluto

The fascinating discoveries of the New Horizons probe have reignited the debate about whether the International Astronomical Union (IAU) was right to delist Pluto from the Solar System’s planetary roster in 2006, and relegate it to dwarf planet status. The vote to do so was tight and our new knowledge could change the debate.

From an astronomer’s perspective it’s not difficult to see why Pluto was delisted. It’s tiny – smaller than our Moon and eight other satellites – and much of Pluto’s mass is thick layers of ice around an even smaller rocky core.

Pluto

Beautiful … New Horizons’ snap of Pluto

It’s also got a vastly elliptical orbit around the Sun, unlike any other planet. However, more importantly from the IAU’s perspective, is Pluto’s position. The 2006 vote came from the IAU actually defining what a planet is for the first time. This might seem obvious but, if you look at the Solar System, that’s not the case – it’s actually very complex.

An Interesting Mix

For example, the eight current planets are very different. The first four, Mercury, Venus, Earth, and Mars, are all rocky bodies with clearly defined surfaces. The next four, Jupiter, Saturn, Neptune, and Uranus are gas giants with no such features.

The IAU came up with three defining characteristics of a planet in our Solar System. It must be in orbit around the Sun, have a spherical shape, and have “cleared the neighborhood” around its orbital plane of other bodies. It’s that third test that Pluto fails on.

Pluto sits at the inner edge of the Kuiper Belt, a collection of icy bodies on the far edge of the Solar System. In 2005 the dwarf planet Eris was discovered out beyond Pluto, and has about 27 per cent more mass than Pluto.

Seen It Before

Astronomers have been here before. In 1801, improving telescope technology enabled Catholic priest Giuseppe Piazzi to spot a body between Mars and Jupiter, which became known as the planet Ceres. Similar bodies called Juno, Pallas, and Vesta were also spotted nearby and added to the planetary roster.

But as more and more bodies like these in the general vicinity were spotted, astronomers declassified them as planets and clumped them together as the Asteroid Belt. Now the same thing is happening with Pluto, as we spot more and more objects in the Kuiper Belt.

Not so fast, says NASA and others

Stern’s comments on Friday come as no surprise: he’s been one of the most vocal voices of dissent ever since the 2006 IAU vote and said at the time that “the definition stinks.”

Most of the planets in the Solar System, Stern correctly pointed out, don’t have clear orbits – there are plenty of asteroids in the vicinity of Earth, Mars and Jupiter’s orbits. He also noted that fewer than five per cent of the astronomical community actually voted to delist Pluto.

Stern is rather biased – after all, the vote came as New Horizons was speeding towards Pluto after its lift off earlier that year. But he does have a point too – we now know Pluto is a highly complex piece of geography and has none of the blandness of Ceres or Vesta. And he’s not alone.

Here in the US both New Mexico and Illinois have passed legislation that has explicitly defined Pluto as a planet. Pluto’s discoverer Clyde Tombaugh was from Illinois, by the way, and some of his ashes are flying on the New Horizons probe as it speeds into the Kuiper Belt.

There’s certainly a lot of public support for re-entering Pluto in the planetary roster, so much so that noted astronomer Neil DeGrasse Tyson has given lectures devoted entirely to telling Pluto supporters to “get over it.”

Past Experiences

Part of the support for Pluto as a planet is, no doubt, cultural conservatism. We all grew up considering Pluto a planet and it’s nice to carry on thinking that way. But, as we’ve found at El Reg, that’s not the only reason.

Take Reg scribe Kieren McCarthy, who has a daughter born after Pluto was declassified. She’s become so entranced with the recent news from Pluto that she writes letters to scientists asking for it to be reinstated again, based on how fascinating the place is.

Many More Plutos

As we learn more about Pluto and the Kuiper Belt, this debate over Pluto’s planetary status is only going to get more frenzied. Certainly Pluto is a very complex orbital body, but it may be that there are other similarly intricate bodies out in the Kuiper Belt.

New Horizons is now on its way to find out what some of these rock lumps look like. If they are just dull snowballs, then Pluto might be readmitted into the Solar System. That’s how science works – you find stuff out and apply it rather than relying on faith and dogma. Source: The Register

NASA’s Epic Pluto Flyby Almost Didn’t Happen on Time

NASA’s New Horizons spacecraft got the first-ever up-close looks at Pluto this month, but the epic encounter very easily could have been delayed by a couple of years. Scientists and engineers had to work at breakneck speed to get New Horizons launched during a brief window in January 2006, said mission principal investigator Alan Stern, of the Southwest Research Institute in Boulder, Colorado.

Missing this three-week window — which enabled a speed-boosting flyby of Jupiter in 2007 — by even a few days would have pushed the July 14 Pluto close approach into 2016, Stern said. But the team’s hard work paid off, and New Horizons zoomed past Pluto on time.

“We did it,” Stern said here Sunday (July 26) at the Intrepid Sea, Air and Space Museum, during a talk at the fourth annual Space and Science Festival. “We worked nights and weekends for four years.” During the talk, he gave the audience some insights into the history of New Horizons, and what makes the mission special.

New Horizons was one of several Pluto missions that scientists proposed and developed beginning in the 1990s, Stern said. At the time, researchers were beginning to learn that Pluto was not some lone, icy oddball, but just one of many objects orbiting in the distant Kuiper Belt, which lies beyond Neptune. That realization made the scientific case for a Pluto mission stronger, Stern said.

“In the 1990s, we discovered Pluto’s context — the third zone of the solar system,” he said. With a total cost of $723 million, New Horizons is much cheaper than the Voyager program, NASA’s last effort to explore the solar system’s outer reaches. (The Voyager 2 probe made history’s first flyby of Neptune in 1989.) Space.Com

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