Thoughts on the 9th Planet

The internet was abuzz last week with news of a possible 9th planet in our Solar System, as well as an opportunity to view all five planets visible to the naked eye in the sky at the same time for the first time in more than a decade. Coming on the heels of the BBC StargazingLIVE show, and ongoing coverage of Tim Peake's mission oboard the International Space Station) it feels like space and astronomy has never been more at the front of the UK public’s consciousness.

The possibility of the discovery of a new planet so close to us might seem to make a mockery of how much we claim to know about the vast expanse of space. You might ask how we can claim we understand the structure of galaxies in the distant Universe when we have potentially missed an entire planet in our own solar system for so long. But this planet, if it turns out to be real, will be very dark indeed. The predictions suggest it orbits the Sun, 20 times further out that Neptune (which in turn is 30 times further out than the Earth). At this distance the planet would take 10,000-20,000 years to orbit the Sun, moving incredibly slowly against the background stars. And the illumination from the Sun would be over 300,000 times less than it is here at Earth, making it both a very cold and dark place, as well as an incredibly hard thing to spot with a telescope. Astronomers all over the world will now be searching for this tiny speck of light, in an interesting parallel of several previous searches which have happened following earlier predictions of missing planets (these earlier searches led to the discover of Neptune, as well as Ceres and Pluto – two objects we now consider dwarf planets, but which we initially called planets). 

Of course the last time the number of planets in our Solar System was in the news we all had to come to terms with losing a planet. Pluto is still exactly where it always was, but in 2006 was reclassified as a dwarf planet following the discovery of potentially hundreds of Pluto like objects in the outer solar system. As an astronomer it never fails to surprise me how much this reclassification, which you might dismiss as an obscure technical discussion, captures the public imagination. This has recently been back in the news following the amazing pictures of Pluto sent back by the New Horizons Mission. While I’m often surprised at the interest this generates, I’m also pleased for the opportunity it gives to remind us all that science isn’t a fixed and static thing. We reclassify planets on the basis of new information, and we can still have the opportunity to discover massive new planets in our own backyard. 

The already iconic view of Pluto from the NASA New Horizon's Mission.

If you want to see all six planets visible to the naked eye at once (Mercury, Venus, Earth, Mars, Jupiter and Saturn) you can get up early on any clear morning over the next month or so. Venus and Jupiter will be the two brightest points of light you can find in the sky – Jupiter is to the West, and Venus to the East. In a rough line between them will be the noticeably orange tinged Saturn and Mars. Mercury is a challenge as it’ll be a small point of light fading into the dawn light as the Sun rises – of course Earth you can see all the time (just look down). 

A screenshot from the free planetarium software Stellarium showing all 5 visible planets together in the sky at 6.50am on Tue 26th Jan 2016

 

To see the International Space Station and wave at Tim Peake as he passes by, you can look for notifications of the next visible ISS passesonline. The next ones visible from where I live (in the UK) are Feb 2nd and 3rd in the evening. The ISS looks like a steadily moving constant point of light to the naked eye, and you see the reflected sunlight off its solar panels.

School visit: scale of the Universe

I went on a school visit this week to Springfield Technology College - a secondary school with a focus on science/technology just to the north of Portsmouth.

Kudos to the teachers at the school for suggesting I speak with two groups one after another - thus giving me maximum outreach impact for my travel.

The first group I spoke with was 60 YR7 pupils (11 and 12 yr olds). I chose to talk to them about "The Scale of the Universe" as it allows me to talk about planets and use my fun solar system model, but also link to cosmology and the types of science we focus on here in Portsmouth ICG.

I started with the inflatable solar system model. As previously used at out BBC StargazingLIVE Event at the Spinnaker Tower, and already on their 3rd school visit.

Inflatable planets decorate the Spinnaker Tower (in an approximation of the actual layout of the Solar System in Jan 2012). 

To introduce this to children I start with the Earth. I ask them to think about distances they are familiar with. I ask things like who has been on holiday a long way away, and if anyone has done any long walks or car rides. I then ask them to imagine shrinking the whole Earth down to the size of the model. I ask for a volunteer to hold the Earth.

I should point out at this point, that while the inflatable solar system is pretty fun as a demo, it's not an accurate scale model in any sense. I made the below cheat sheet for myself to remember the real relative sizes.

On the scale of the Earth in the model, the Sun should be 36m across. This isn't too far of the scale of the classroom which I will point out. Obviously it's not possible to have a beach ball that big, so we'll use the one provided (which is almost a metre in diameter and which they were very keen to get picked to hold!). On this scale the Earth should really be about 1cm across (and I have a little ball on a cocktail stick which is about this size). I next suggest the student who is holding the sun that he walk about 1km  away to make an accurate scale model (just kidding!). From Springfield school this was about the distance to the train station which was useful. So instead we won't really make a scale model, but we'll put the planets in order. Then I let them pick planets they like and tell them a little bit about each one in turn (if you can see it, some tiny fact).

I'll usually demo the real Earth-Moon distance when that comes up - asking them to tell the student holding the Moon how far away it should really be (they always guess too close - as would have I before seeing the real answer).

After this part of the talk I moved to videos. I showed them the real scales of the planets using a video. You can find lots of these on YouTube (which I downloaded using an internet service in case I couldn't get online for the talk). The one I used is this one:



Which I stopped at about 55 seconds on the image of the Milky Way. So then I talked about galaxies - about how many stars might be in each galaxy and how most of them probably has a planetary system.

To go further up in scale I use the fly through of the Sloan Digital Sky Survey DR4.



Which is great because ICG are involved in this survey (which I meant to tell them, but I think I forgot). It also ends with the CMB so we could talk a bit about cosmology and the birth of the Universe.

At this point I get a lot of questions. Mostly on cosmology - what's before the Big Bang, outside of the Universe etc. great questions. After a while of that I remind them they can ask me about other topics in astronomy - doesn't anyone want to know about black holes or aliens. Which led to a discussion of spaghettification. Always fun - especially when you're 12! Final question - what would happen to a plate of spaghetti which fell into a black hole (and we find out the class joker!).

To end I gave out my colour the solar system scale model - perhaps a bit young for them, but you never know. I made a new version you can print on just one sheet of paper.

I enjoyed it and I think they did too.