When Year 8 College student, Sarah Liu, asked the question, ‘What would happen if we took one of the planets from our solar system?Would it mess up the solar system or would it remain the same?’, she started a chain of questioning that began in her Year 8 classroom at College, moved to the physics labs in the Science Block, progressed to the Librarian at NASA Headquarters in Washington, who was stumped by the question, and finally drew a response from an astronomer at the NASA Jet Propulsion Laboratory at the California Institute of Technology! This was followed up by an answer from our own physics teachers once they’d had time to reflect on Sarah’s request.

The Year 8’s had been studying the solar system as part of their new science topic looking at the different planets and their orbit. A recent visit from Starlab, a mobile planetarium, had set the scene for probing questions about the solar system. Sarah’s seemingly simple question highlighted the importance of continuing to probe and question in search of an answer.

Not so long ago, students would have turned to a set of printed encyclopedias for an answer, or written a letter that would arrive and return in its own good time. Now, our students have information online at their fingertips, although with a question such as this, the answer may not always be so easy to find. Emails have changed the way we communicate and so Sarah, her teacher, Mrs Catherine May, and her classmates were tickled pink when staff at NASA took the time to consider Sarah’s email and respond.

The first to respond, Rick Spencer, the Information Services Manager at NASA Headquarters admitted to being stumped and so passed the question on to Stephen Edberg, an Astronomer at the NASA Jet Propulsion Laboratory at the California Institute of Technology. Stephen’s response was similar to that from our own physics teacher, Mr Hamish Wilde that, in essence, not a lot would happen, however, Mr Wilde made a very pertinent point, ‘The biggest cost to humanity would probably be, once again, rewriting all the astronomy books and web resources to reflect the change to there now only being 7 planets in the solar system!’

Read the Sarah’s email and the responses below:

Sarah’s question to NASA:

Dear NASA

This question is for one of your experts...

‘What would happen if a planet was removed from our solar system? Would it mess up the solar system or would it remain the same?’  This is the question I wanted to ask but can't seem to find an answer to this online. So I was wondering if one of your experts could help me on this very interesting question that my class and I are bursting to know. 

At school right now we are learning about the solar system as our new topic for science and the teacher asked us to write down some questions we had about the solar system and to research them. 

Yours Sincerely,

Sarah Liu
(Year 8 Student)

Response from the Information Services Manager at NASA Headquarters:

Dear Sarah

Thank you for your email and intriguing question. Congratulations, you have won ‘Stump the NASA Librarian.’ I haven’t been able to find an answer! So, I have forwarded your email to a few contacts I have here at NASA. They may respond directly to you or they might reply to me and I will forward you the answer.

I suspect that the answer will depend on a few additional questions such as, ‘How is the planet removed?’ and, ‘Which planet?’ Since Mercury is very small, its loss from the solar system would likely have little effect on the other planets. However, if Jupiter disappeared, there could be significant changes. Jupiter is more than twice as heavy as all of the other planets and their moons combined (also, what would happen to Jupiter’s 50 moons?). Similarly, Saturn is more than twice as heavy as the other planets and their moons combined (excepting Jupiter, of course) and it also has more than 50 satellites.

Thank you again for your email. I am hoping that one of the scientists can respond to both of us because it is a very interesting question.

Yours,
Rick Spencer

Richard Spencer
Information Services Manager, BFJV, Inc.
Library, Information Center, Historical Reference Center
NASA Headquarters
300 E St. SW, Rm 1W53
Washington, DC 20546
http://www.hq.nasa.gov/office/hqlibrary

Response from an Astronomer at the Jet Propulsion Laboratory in Pasadena, CA. 

Dear Sarah

In short, there would not be major changes to the Solar System if a planet was instantaneously removed. However, a more detailed answer would include a discussion of over what period of time we are talking about. A few million years, a few hundred million years, or over the age of the Solar System?

Your question about the effect on the Solar System of removing a planet is one that is very interesting to researchers, addressed in a different way. It is asking “How stable is the Solar System?” The answer may surprise you. 

Western civilization has considered the Solar System to be much like a big clock (you’ve probably heard the phrase “the clockwork of the heavens”). That dates back to at least the 1600s and perhaps much earlier. In the 1600s Johannes Kepler discovered what we now call Kepler’s Laws and Isaac Newton proposed and demonstrated the workings of the Law of Gravity, which explained the motions of the planets including Kepler’s Laws. 

Flash ahead to the recognition of chaos theory and the invention of BIG computers and efficient algorithms for handling large amounts of data. Now researchers can run simulations tracking the motions of planets, dwarf planets, moons, and asteroids as each influences the motions of all the others. Monte Carlo simulations (meaning to test lots of different starting conditions) allow researchers to really see how the Solar System might behave. 

Testing the stability of the Solar System has shown that, in fact, the Solar System does not have to stay stable indefinitely. Small changes in orbits and masses, or in our knowledge of those orbits and masses (that’s why Monte Carlo simulations are run) can lead to changes in the long term that can be quite abrupt considering the time scales involved. 

For instance, there is evidence that during the first few hundred million years of the Solar System’s existence, the giant outer planets were migrating in and out compared to their current distances from the Sun. The churning cleared most of the inner Solar System of the remaining planetesimals that combined to create the planets. Uranus and Neptune probably started their existences much closer to the Sun and as they migrated out they sent planetesimals in more distant orbits either into the Sun or out of the Solar System. Saturn may have been inside the orbit of Jupiter. All four of them moved around before settling into the orbits they have now. The orbits of all the planets could change significantly over geological time scales in the future. 

So removing a planet might not change things over short (a few million years) time scales but things could change a lot over longer periods. 

Keep asking good questions like this! 

Best wishes,
Stephen Edberg

Astronomer
NASA Jet Propulsion Laboratory
California Institute of Technology

Response from Mr Hamish Wilde, Physics teacher at Saint Kentigern

Dear Sarah

Removing a planet won’t do a whole lot – there is mostly empty space in the solar system after all.  The orbits of the other planets will be largely unaffected as gravity between each planet and the sun is so much more significant that that between any two planets (even adjacent planets)

Removing Jupiter or Saturn may alter the course of regular orbits of comets that pass deep into the solar system then go back out again towards the oort cloud. But chances are the effects would be rather hard to detect.

If you blow up a planet you basically get what there is between Mars and Jupiter – an asteroid belt where all the remaining chunks of a planet or planetoid continue to orbit in the same region of the solar system.

The biggest cost to humanity would probably be, once again, rewriting all the astronomy books and web resources to reflect the change to there now only being 7 planets in the solar system!

Hamish Wilde
B.E (Hons), Dip.Tch
Science and Physics Teacher, Saint Kentigern College

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