Institute of Astronomy

 

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Habitable planets

Published on 08/11/2013 
Question: 

Two questions, which are linked.

Occasionally there is some coverage in the media about the continuing discovery of planets around other star systems in the Milky Way, through the work of the Kepler telescope, and other initiatives. Is there a place on the web I can go to, to check what the latest thinking on all of this work is? I'm thinking of an up to date receod of things like numbers of candidate habitable planets discovered, where they are, stuff like that.

Second question, is there any work being done to try to identify such planets around either Alpha Centauri A or B? Is there somewhere I can go to on the web to see what the current thinking and evidence is from any work on these stars and their surrounding planets, and whether any might be in the 'goldilocks' zone for these stars?

There are several websites that maintain catalogues of exoplanet discoveries, with the two most well known being the Extrasolar Planets Encyclopedia (www.exoplanet.eu) run by Jean Schneider at the Paris Observatory, and the Exoplanet Data explorer (www.exoplanets.org) run by NASA, both of which provide facilities for plotting some of the basic parameters of the planets.  Both of those catalogues also have links to other pages about exoplanets, including things like discussion of potential habitable zone planets (though on that particular point be warned that there is no definitive agreement about the location of the habitable zone so you will likely find significant differences between different sources).

Alpha Centauri, as you can imagine being the nearest star system to our own Sun, has been extensively studied for many years to determine whether it has planets.  Last year a roughly Earth-mass planet was reported around Alpha Cen. B orbiting at 0.04AU (about a tenth of the orbital distance of Mercury), however there is considerable controversy surrounding this discovery and it has yet to be confirmed.  The existence of any planets larger than around Neptune has already been ruled out in the Alpha Centauri system, however finding, or ruling out, small, Earth-size, planets at Earth-like orbital distances is exceptionally difficult.  The Wikipedia article on Alpha Centauri Bb actually does a very good job of summarising the current situation.

Comet C/2012 S1 (ISON)

Published on 08/11/2013 
Question: 

If Comet Ison were to break up passing close to the Sun, Would the pieces of the comet emerging from around the Sun, Could those various size pieces somehow Shotgun the Solar System?

The tidal break-up of a comet is, in astronomical terms, a comparatively 'gentle' event and the various fragments of the comet would continue on very similar orbits.  The comet Shoemaker-Levy 9 that impacted Jupiter in 1994 is a very good example.  When it collided with Jupiter in July 1994 it did so as a string of at least 21 fragments as a result of having been tidally disrupted during a previous close passage of Jupiter 2 years earlier.  After the tidal disruption event all of the fragments retained nearly the same orbit such that they all collided with Jupiter over the course of 6 days in July 1994.  More directly similar to the comet C/2012 S1 (ISON) is the Kreutz family of sungrazing comets, which are all believed to have originated from a single large comet that fragmented during a close passage of the Sun.

As a side note, the correct designation of 'comet ISON' is C/2012 S1, the (ISON) appended after the designation just indicates the organisation that discovered it, in this case the International Scientific Optical Network, based in Russia.  It might seem somewhat pedantic, but the ISON team will discover other comets (it is what they do), so there will be other comets with the suffix (ISON).

Microscopic life on other planets

Published on 27/08/2013 
Question: 

I was reading lots on the planets and the atmosphere around them. We have detected creatures in the icy lakes and in very hot areas. I was wondering can there be life on other planets. They may not be aliens but some sort of creatures living on other planets. And if so yes, how could they live on other planets?

The most likely kind of 'aliens' are indeed bacteria and other small micro-organisms similar to the ones that we have found in extreme environments on Earth, such as frozen lakes, hot springs and thermal vents.  There are long term plans to send a mission to Jupiter's moon Europa to search for just this kind of life.  We know that Europa has a liquid ocean beneath it's icy surface, and the geological activity induced by the tides from Jupiter may well result in thermal vents very similar to those found on the ocean floor near mid-ocean ridges on Earth.

Pretty much everywhere we look on Earth we find life that has adapted to living there, and we can see places elsewhere in the solar system that look like they may have environments similar to ones we have found life in on Earth.  Sending missions to these places and finding out whether they also have life will tell us a lot about how common life is in the universe, and how life evolved on Earth.  Missions like that are very complicated, and expensive, however, partly as we need to make sure that they don't accidentally take any Earth life with them.  It would be rather annoying to have sent a mission millions of kilometres only to detect bacteria that have hitch-hiked from Earth!

Blowing up Jupiter

Published on 06/08/2013 
Question: 

In a hypothetical scenario, if you could bear that in mind I am interested in the effects that would happen to Earth if Jupiter in a hypothetical situation exploded. What kind of magnitude would it be referenced under? And how would the astronomical community report that/those findings back to natons around the world? Would the asteroid belt be perturbed in any way? Shooting out asteroids from it and rocky debris in closer orbit with the gas planet? Your help in this matter to keep your hypothetical hat on just to humour and bear with me would be appreciated, thank you...

It depends in part what you mean by 'exploded'.  The solar system planets are quite widely separated, so at least initially, the effect would be rather small.  The orbits of the other planets would remain close enough to their present orbits that only astronomers would be able to tell the difference, and this will be true whatever type of 'explosion' you want.  As for any immediate, direct effects of the 'explosion', remember that space is a vacuum and so shock waves (sound, earthquakes, etc.) can't propagate.

If we go with a minimal 'explosion' and just magically cause Jupiter to vanish then the only other thing we would have to worry about is what happens to its moons and the asteroids.  The large moons that orbit close to Jupiter would probably all simply be ejected from the solar system and not pose any threat to anyone.  Some of the smaller ones further out might go onto elliptical orbits around the Sun, but there are not that many of them so the chance of a collision would be quite small.  The asteroid belt would likely remain much as it is, interactions with Jupiter actually generally serve to destabilise asteroids rather than the other way around.  The only possible cause for concern would be the Trojan asteroids, which share Jupiter's orbit and lead or follow it by 60 degrees.  These occupy stable regions created by the gravity of Jupiter, so if Jupiter were to disappear some of them might become unstable and come into the inner solar system.  This would likely be a long process rather than a fast one so we would probably have a reasonable length of time to deal with any new asteroid that appeared on a collision course with Earth and not be much worse off than our current situation.  In short, other than the disappearance of Jupiter from the sky, most people probably wouldn't notice the difference.

Now, on the other hand, if you want a 'Death Star' style explosion rather than just a planetary vanishing act things would be a little different.  Jupiter is extremely massive, and all of that mass suddenly flying around the solar system is going to have some rather interesting effects.  Now most of the mass of Jupiter is gas (primarily hydrogen and helium), which the Sun would eventually blow away through X-ray radiation and the solar wind (though it might take some time to do so).  What effect the gas has depends partly on how far the explosion spreads it and so how dense it is, it could potentially exert drag on some asteroids, particularly the Trojans, and cause them to spiral in to the inner solar system.  If Jupiter has a rocky core (we aren't actually entirely certain if it does), then that would cause additional problems.  The core of Jupiter might be as more then 10 times the mass of Earth, by comparison the whole asteroid belt is less than 0.1% the mass of Earth.  Turning all of that into rubble and throwing it across the solar system would cause utter havoc, the conversation between a whole leader and an astronomer would probably go something like this:

Astronomer: Jupiter has exploded, the core, which incidentally we know now was 10 Earth masses, has been pulverized and thrown out across the solar system.
World Leader: That doesn't sound good, is any of it going to hit us?
Astronomer: We haven't determined the exact numbers yet, but we expect the impacts to start within a year.
World Leader: Within a year!?  What kind of damage are we expecting?
Astronomer: It will probably start fairly localised, but the surface will reach saturation quite rapidly.
World Leader: Saturation?
Astronomer: Imagine carpet bombing the entire planet with the largest nuclear weapons you have.
World Leader: Oh... Can we do anything about it?
Astronomer: Nope.
World Leader: So we're doomed then?
Astronomer: Pretty much, yes.

If Jupiter doesn't have a core, or if it is pulverized into small enough pieces in the explosion (think dust), then it might not be so bad.  The gas and dust would probably partially block out the Sun and cause and ice-age, though material raining down into the atmosphere might also cause Earth to heat up, so it might get hotter even with the Sun being dimmed.  Either way the environment would be pretty screwed up but some people might survive.

Number of stars in a galaxy

Published on 24/06/2013 
Question: 

As an astronomer when you look at distant galaxies do you sometimes wonder what it would be like in those galaxies? Perhaps ellipictal and dwarf galaxies not spiral galaxies because our milky way is one of them. Also how do astronomers approximate the number of stars in each galaxy?

It is indeed interesting to think about what it would be like in a different galaxy, or even in a different part of our own galaxy.  Nearer to the galactic centre for example there would be many more stars in the night sky.

To approximate the number of stars in a galaxy essentially what we do is look at how bright the whole galaxy is and then divide that by the brightness of an individual star.  There are additional things we do to make it more accurate however, not all stars are the same mass and brightness for example, and there may be dust in the galaxy obscuring some of the stars, but we can look at the spectrum of light from the galaxy (how bright it is at different wavelengths) to help us disentangle these problems.