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Welcome to the family, Pluto

by Tanya Hill
Publish date
16 July 2015
Comments (3)
image of planets Welcome to the family. Ben Gross/twitter, CC BY-SA

What an amazing time for space exploration. The picture of the solar system from my childhood is now complete, as seen in this great family portrait produced by Ben Gross, a research fellow at the Chemical Heritage Foundation, and distributed via twitter.

I love this image because it shows each world in close-up, using some of the latest pictures from space exploration. As we celebrate seeing Pluto for the first time, it’s remarkable to think that this completes a 50 year task.

It has been NASA that has provided the first close-up views of all these worlds. Here’s the rundown:

  • Mercury: Mariner 10 (1973)
  • Venus: Mariner 2 (1962)
  • Mars: Mariner 4 (1965)
  • Jupiter: Pioneer 10 (1973)
  • Saturn: Pioneer 11 (1979)
  • Uranus: Voyager 2 (1985)
  • Neptune: Voyager 2 (1989) and
  • Pluto: New Horizons (2015)

But science never stays still. When New Horizons left Earth in January 2006, Pluto was a planet. Later that year an important reassessment was made of the Solar System and Pluto became the first of the dwarf planets.

The ‘Not-Planets’

The Planetary Society’s Senior Editor, Emily Lakdawalla, has teamed together the ‘Not-Planets’. These are the close-up views, shown to scale, that have been captured of the largest moons, asteroids and dwarf planets.

image of non-planets in the solar system Montage by Emily Lakdawalla. The Moon: Gari Arrillaga. Other data: NASA/JPL/JHUAPL/SwRI/UCLA/MPS/IDA. Processing by Ted Stryk, Gordan Ugarkovic, Emily Lakdawalla, and Jason Perry.

It clearly shows that there are many diverse and interesting worlds to explore beyond the eight planets of our solar system.

New Horizons is the first spacecraft to start exploring the Kuiper Belt, an icy realm of objects orbiting 5 billion kilometres or more beyond the sun. It’s the chance to observe a dwarf planet, something distinct from the terrestrial planets and the gas giants.

It was in 1992 that astronomers discovered Pluto was not alone. The first Kuiper Belt Object, designated 1992 QB1, is a 100-kilometre sized object that orbits well beyond Pluto.

Now more than 1,000 objects have been detected in this realm, and the belt likely contains many more. Most are small compared to Pluto, but there are some stand-outs such as Quaoar, and the dwarf planets Eris, Makemake and Haumea.

Don’t forget to phone home

The suspense of the mission has certainly been high. To maximise the amount of data that New Horizons could collect, the spacecraft did not communicate with Earth for the duration of the flyby. As described by Mission Operations Manager Alice Bowman, it was the moment when you let your child free.

The team had prepared New Horizons, told it what work needed to be done and in that radio silence they had to trust that all would go to plan.

Just before 11am today (AEST), New Horizons checked in – showing it to be the perfect child to the relief of its many anxious “parents”. It was only a brief phone home, but in that short time the scientists confirmed that all telemetry was spot-on, the spacecraft followed the path that had been set for it and there were no error messages recorded on any of the systems.

No data was transferred in that brief connection, but it was established that the main computer system, which records all the data collected by the spacecraft, showed the expected number of segments had been used. In other words, data had been collected.

We will soon see Pluto and Charon in even higher resolution. Their geology will be mapped, the surface compositions and temperatures will be measured, atmospheres will be probed and new discoveries will be made.

A love note from Pluto

It’s also been wonderful to see the public become so enthralled with the latest image from Pluto. Humans are incredibly good at spotting patterns and it seems that Pluto wears his heart on his sleeve for us.


I’m also equally intrigued to discover that the smooth part of Pluto’s heart is made of carbon monoxide ice. This was already known from ground-based observations, except never before seen in such detail. It’s reassuring to have a good match between the old and new data.

But look again … is it a heart or something entirely different stealing the show?



Tanya Hill is Honorary Fellow of the University of Melbourne and Senior Curator (Astronomy) at Museum Victoria.

This article was originally published on The Conversation. Read the original article.

The problem with Pluto

by Tanya
Publish date
18 February 2013
Comments (0)

On 18 February 1930, Clyde Tombaugh achieved an amazing feat - he discovered Pluto. It’s said that he was a meticulous astronomer and I’m sure he must have needed all that mettle to have stumbled upon the tiny speck that was Pluto.

Over six years ago, Pluto grabbed headlines when astronomers famously ‘demoted’ the planet and designated it as the first of the dwarf planets. Some were disappointed by this – but I have to say that Pluto has always been a bit of an odd-ball. It was something we had explored a year earlier with the release of our planetarium show, The Problem with Pluto, in 2005.

The Problem With Pluto In this planetarium show, Lucy is on a research craft with her mother Lillian, a scientist, and together they are gathering data to discover just what Pluto’s status should be.
Image: Melbourne Planetarium
Source: Museum Victoria

A fellow astronomer shared with me his interesting way to explain it. Imagine, as a child, having a case full of pencils. The pencils came in all different colours but at their heart they were the same; except for one. It was a bit odd, still good for colouring-in just like a pencil, but there was something different about it. Nonetheless, it was the only one you’d even seen and it had always been in the pencil case, so you called it a pencil along with all the others. Then, one day at a friend’s house, you opened their pencil case and it was filled with something called crayons. Your eyes lit up with recognition. That odd-ball pencil you’d been worried about wasn’t odd after all, it was in fact a crayon.

When Pluto was discovered, it was one of a kind at the edge of the Solar System. It wasn’t a terrestrial planet, it wasn’t a gas giant, but it did orbit the Sun. Seventy years on, we now know of thousands of objects orbiting alongside Pluto. They are the icy worlds that make up the Kuiper Belt. Pluto, because it is big enough to be round, is still a bit special and so it now goes by the new label of dwarf planet.

On Pluto Day, I’ll be celebrating that Pluto has now found its rightful place in the Solar System.

New Horizons spacecraft Right now, a real research craft is on its way to Pluto. Called New Horizons it will fly by Pluto in July 2015 and journey on to discover more about the Kuiper Belt.
Source: NASA


The Problem with Pluto will be showing at the Melbourne Planetarium at 2pm, 18 February to 4 March.

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