Archives For Solar System

Line 1. Let’s start with ‘typical’ humans. The average human adult male is 1.75 metres tall – that’s 3.83 cubits or 5.74 feet. The average female is 1.62 metres – that’s 5.4 light-nanoseconds or 0.008 furlongs.

20141126 - RJS - Stargazing Scale.002

You live on Earth (Sol d, perhaps?). This is an Earth-like planet in a Sun-like star system. The third planet of eight in a rich system, including a least one planet populated entirely by robots (Mars, perhaps?). Earth is 12,742 km in diameter and thus has a circumference of 40,000 km or roughly 25,000 miles. Humans live in a thin layer (~20km) around the surface called the troposphere. If the Earth was a beach ball then all life on Earth exists within just 1mm around the surface.

20141126 - RJS - Stargazing Scale.004

Through many years of international effort we have managed to keep a ‘space’ station in orbit – just above this troposphere – 1cm above the beach ball. But not high enough up that it can totally avoid the atmosphere – the ISS has to constantly boost itself back up because of air drag. We have sent just 24 people out into deep space, beyond the Earth’s atmosphere. All of then visited the Moon and the last ones returned in 1972: 42 years ago. They were all men, all white, and all American. We could do it again, we could do it better – but we chose not do so. (Mostly for political reasons IMHO.)

20141126 - RJS - Stargazing Scale.008

Those astronauts visited the nearest body in space: the Moon – the second brightest thing in the sky . They were kind enough to return some photos to show us how teeny tiny we are, and how delicate out world really is. The Moon sits about a quarter of a million miles away (384,000 km). You could fit all the Solar System’s other planets in that gap.

20141126 - RJS - Stargazing Scale.012

But that doesn’t include the Sun – the brightest thing in the sky. The Sun is truly huge. You can fit the Earth inside the Sun a million times. It has more than enough room for all the planets and then some. The Sun itself sits 93 million miles away – which means that light takes 8 minutes to reach us from the Sun. The Sun could have gone out 7.9 minutes ago and you’d only find out… now. Nope: we’re ok. For now.

20141126 - RJS - Stargazing Scale.013

And yet we have flung robots into space and downloaded the images they have recorded. Sometimes we take extremely long-range selfies of a sort. Images of the Earth, of humanity reduced to a pixel or two. Here’s one from Mars, one from Saturn and one from out near the edge of the Solar System – taken by Voyager. These images collectively earn us the moniker ‘pale blue dot’. Out by Pluto, the Sun itself is has dimmed to look like an other stars. From Saturn, we are just a couple of pixels as seen by the Cassini probe:

20141126 - RJS - Stargazing Scale.017

And truthfully, the Sun isn’t so special. In fact there are stars which make the Sun look even smaller than the Earth does here. VY Canis Major is staggeringly big – and could encompass the Sun 1,000,000,000 times. That’s a million trillion Earths. Oh and VY Canis Major isn’t even visible to the naked eye because it’s so far away that we can’t detect its photons without aid of telescopes or binoculars.

Which brings us to the Galaxy. The Sun is just one of hundred of billions of stars orbiting around the Milky Way. If the Sun was a blood cell then the Milky Way is the size of Europe. The Milky Way is staggeringly big also staggering diffuse – so much so that if you took two Milky Ways, and hit one with the other, then in all likelihood no two stars would collide. They would pass though each other like smoke.

In fact this will happen. The Andromeda galaxy – which is a lot like the Milky Way – is on a collision course with us. In about 4 billion years it will begin to merge with our galaxy in a spectacular collision. We see these happening elsewhere but the sheer scale of this vision in our own night sky makes me want to get a time machine and jump forward to see it happen. The Earth is unlikely to be affected by this, because of the lack of collisions – however our night sky will be spectacularly altered for hundred of billions of years. Makes you realise how dull it is right now. Just kidding!

654291main_p1220bk

But the Milky Way and Andromeda are just two out of hundred of billions of galaxies in the Universe. Gigantic stellar continents floating in a vast, void of almost nothing. Galaxies themselves form structures, and as we have looked deep into the cosmos we have seen one such structure: the Sloan Great Wall. A thick chain of galaxies, loosely bound to each other by gravity, stretching 1.4 billion light years across the Universe and about 1 billion light years from the Milky Way. It’s 1/60 of the Universe across. And yet there are even bigger thing out there.

20141126 - RJS - Stargazing Scale.026

The largest known structure in the Universe is the Hercules–Corona Borealis Great Wall. At 10 billion light years across, this huge filament of galaxies in 1/10 the size of the observable Universe. It’s 100,000 time the size of the Milky Way, and 70 million trillion times bigger than than the Sun. We don’t have a good picture of it, but we know it’s there. It’s 7,000,000,000,000,000,000,000 times bigger than the Earth, which is very much bigger than you. I refer you to line 1.

KOI-351

We recently posted news of a Planet Hunters planet discovered as part of a seven-planet system. Like all the Planet Hunters stars this is one seen in data from NASA’s Kepler spacecraft. Dubbed Kepler-90 this system is a peculiar microcosm of our own Solar System, with small (probably rocky) worlds in the middle, and larger (probably gaseous) worlds on the outside. The major different being that the outermost planet in this system is as far from the star as Earth is from the Sun. The other six planets in this system were already known about, but thanks to volunteers on Planet Hunters (http://planethunters.org) we now think that there are seven worlds circling this stars, which is just a little brighter than our Sun.

New PH Planet

To celebrate this fact I have created a model of the whole planetary system in Celestia, an awesome, cross-platform, open-source package that lets you explore space. You can download the Celestia files model directly here or watch the video below to be taken on a tour of Kepler-90 and it’s seven worlds.

In this video, I’ve given the newly discovered Planet Hunters candidate some fetching green rings – which we do not have any evidence for or against. Also keep in mind that we know very little about what most exoplanets look like, so we’ve used artistic license to give them all different appearances, often using the surface of what might be analogue worlds in our Solar System. Maybe you can spot some familiar surfaces amongst them!

This system has some great features that make it interesting. The outermost world is roughly the the size of Jupiter but orbits at almost exactly the Earth-Sun distance of 1AU. A Jupiter-like world in an Earth-like orbit has been seen before in Planet Hunters discoveries. The middle planet in this system is at the same distance from this star as Mercury is from our Sun, but is six times as large. The rest of the planets whizz around in even smaller orbits. This star is a little hotter than our Sun so they are pretty scorching places with surfaces temperatures in the hundreds of degrees – nearly a thousand for the innermost planets.

Inner System of KOI-351

The two innermost planets are roughly Earth sized and are really cool. The innermost one is 1.02x the diameter of Earth and the next is 1.18x. We assume that they are both rocky since they are so small. They orbit the star in just 7 days and 9 days respectively and are very close together. So close in fact that if you’re living on the inner, smaller planet then every few weeks, for about a week, the second planet appears in the sky about half the size of our full Moon.

Every year I see the rumour going round that Mars is going to be as big as the full moon. It will never happen for us – but on the tiny worlds circling Kepler-90, it happens all the time.

Update: The system used to be called KOI-351 but was given the name Kepler-90 just a day after this post went live. I have updated the name of the system in the text.

[Cross-posted on the Planet Hunters blog]