Institute of Astronomy

 

Ask an Astronomer - Solar System

Definition of Meteoroid vs Meteorite

Published on 03/01/2013 
Question: 

Does a meteoroid have to become a meteor first, before being defined as a meteorite when reaching the surface of a planet? So, in other words a meteoroid that impacts our moon, which does not have an atmosphere, would never be classified as a meteor. So when it impacts the moon's surface, is it still a meteoroid or meteorite?

There is no requirement for a meteorite to have previously been a meteor.  You are quite right that in the case of something impacting the Moon as there is no atmosphere it will never be a meteor, so it will be a meteoroid right up until it hits the surface, at which point it is a meteorite.

Formation of Earth and life

Published on 07/11/2012 
Question: 

Hello, I was talking to someone the other day and we got onto the subject of Space as it fascinates me, thinking about space and how life began on Earth is the one thing i can't get my head round, thats why it fascinates me. So anyways, I was wondering, is it possible that the planet we know as home, Earth, wasn't always where we are are now? What I mean is, when I try and think how life began on Earth, maybe Microscopic life to begin with yet life doesn't just start. it has to have something to begin with, you cant put a rock into space, leave it for a few million years and then come back and there will be life on it. What I am wondering is, was life on Earth, whatever it was in the start, frozen on a drifting Asteroid, that Asteroid being Earth, kind of like Pluto is at the moment, just a huge planet of ice and rock, though this huge drifting Asteroid of Ice and Rock was glancing past the sun and got pulled into the circular gravitational pull and now rotates. Obviously of Earth was going on a head on course with the Sun it couldn't be pulled into a a gravitational circle as it would be too sharp a turn, though if it was glancing past the sun it could maybee have got pulled into the gravitational pull, then with the heat of the Sun being just right over the years the Sun defrosted this huge block of ice and rock and slowly thawed out the life, almost like the life was in Cryostasis and now its being defrosted, this can happen as theres a certain moth that does this in the Arctic, gets frozen over winter and defrosts and comes back to life in Spring, just wondered if that has every been wondered and what the answer was, that mabye our Earth and life didn't begin where we think it did, instead Earth actually drifted in from another part of space and got caught in the Suns Gravitational pull and the heat defrosted it and allowed life to begin, well not begin, but carry on now its been thawed out, then over the years the speed of the earth rotating combined with it spinning on all axis sort of moulded into a circular shape planet, kind of like sanding it down. Long question I know but it was on my mind, it also seems a bit more plausable, that life didn't begin in the Milky Way, instead the Milky Way is where our planet ended up and thawed out the life that was on it. Just wondered. Btw I don't study Astronomy, just interests me as its the only thing I can't get my head around so I tend to thing about things, so excuse me if this has already been answered. Thanks for your time, all the best

Thanks for your question.  To answer it, it is useful to split it into two parts; 'did Earth form in the solar system?' and 'was Earth the birthplace of the living organisms that now populate it?'

The answer to the first part of that question is almost certainly yes, Earth did form in the solar system.  The process of planet formation involves quite a bit of jostling about so all of the components that went on to form the young Earth did not necessarily come from near the current orbit of Earth but it would be almost impossible to place a rocky planet into the current orbit of Earth by capturing it.  While it is possible for planets to be ejected during formation, space is really very empty and the probability of an ejected planet passing near to another star is very low.  Even if it did happen and the planet was captured it would end up in a very wide very eccentric orbit (similar to a comet) very different to the current orbit of Earth and although orbits do change over time it would be very difficult to change a comet-like orbit into an Earth-like one.

The question as to whether the genesis of life on Earth was indeed on Earth is a very different one and one that has had a great deal of discussion in one form or another for centuries.  If you look up panspermia you will be able to find far more information than I can give you here, though it is good to be aware that there are some rather crazy ideas out there.  It can be something of a controversial topic but as yet no one has come up with a complete theory explaining how life can arise from non-living material either so it is difficult to really say which is the more likely origin of life on Earth.  Anyway the basic idea of panspermia is that life is spread throughout the universe by asteroids and comets, rather like your suggestion.  As well as the suggestion that life first arrived in the solar system by such a mechanism there is the related suggestion that life could be spread throughout the solar system in the same way if it did first arise within the solar system.  As the only place we know of at the moment that has life is Earth it is difficult to make deductions.  Research is being done into investigating how long terrestrial microbes can survive in space, the Russian Phobos-Grunt mission had a small capsule on board that was designed to test whether the microbes contained within it could survive in space for the 3 year length of the mission, but unfortunately, as you may have heard on the news, that ended up in the Pacific.  When we have more experiments like that, or if life is found somewhere else in the solar system, like Mars or Europa, we can begin to answer the question of where life on Earth arose, and how widespread life is in the universe, in more detail.  All we have to go on at the moment is that pretty much anywhere you look on Earth, no matter how extreme, you find life.

Meteor sighting

Published on 24/09/2012 
Question: 

Hi Again. It was not yet completely dark. Just dark enough for cars to have their headlights switched on at about 7:15 pm on 19 Sept 2012. We were travelling north on Airport Way, near Teversham heading towards Quy Waters roundabout. A bright light caught my eye. It was bluey green in colour and it was travelling at the speed of a meteorite but burned longer, maybe 3 seconds. It seemed to disappear perhaps behind a cloud or possibly burned itself out. It looked as if it were heading towards earth at about a 30 degree angle. It seemed significant enough to mention. I was wondering if other people saw it and what it might have been.

What you saw was most likely a relatively large meteor, as you can probably guess the larger a meteor is the longer it will last, and 3 seconds of visibility is not particularly unusual.  Meteors with a blue-green colour are less common, but not by no means unheard of, especially amongst brighter meteors since for fainter ones you won't be able to see the colour (the same reason almost all stars appear white).  The blue-green colour can be an indicator of a higher copper content in the meteor.

Addendum to original reply:
The BBC also picked up on this and Cambridge is far from the only place in the UK the meteors were seen.  One of the astronomers the BBC asked suggested the meteors might have been man-made space junk such as an old satellite burning up on re-entry.  This would otherwise look much the same as a natural rocky meteor, but could certainly explain a high copper content!
 

What happens when asteroids and planets collide?

Published on 10/06/2012 
Question: 

Is asteroid 2003/Q0104 going to hit Earth in May 2031, and if not, then by how much will it miss us and what effect could the near miss have on us; could it hit our moon, and if so, what would the effects be for us?

 

This asteroid is no longer considered to be on a collision course with Earth (or the Moon)! It was removed from this risk category back in 2003 shortly after it was discovered (http://neo.jpl.nasa.gov/risk/removed.html).

If two large objects collide in space, there are a lot of different conditions which need to be accounted for when saying exactly what the effects would be e.g. the size of the objects, their speeds etc.. If the Earth and another object e.g. an asteroid did collide, there are a range of possibilities in terms of the kind of damage it would cause. If the asteroid hit an ocean it would create a mega tsunami while if it collided with land it would cause a large crater, examples of which can be found all over the Earth e.g. Meteor Crater in Arizona, USA. Material thrown up when the crater was formed would also be thrown out of the Earth's atmosphere and would be spread around the neighboring solar system. Depending if the asteroid hit directly or with a glancing blow, this would have a significant effect on the amount of material ejected.

So in summary - there is no reason to panic in 2031! And there are a range of possible outcomes when it comes to collisions of large bodies in the solar system.

Length of a day

Published on 08/02/2012 
Question: 

Hello my name is Sam and I am 11. I have recently got into Science and I done some research and showed my teacher that there wasnt 24 hours in a day. My teacher said that I was wrong and there was 24 hour in a day. could you help me and tell me the real answer to how many hours, minutes and second there are in a day please?

The answer is that you are both right, the problem is what you mean by 'day', and there are two ways of thinking about it.
One way is the length of time between the Sun appearing in the same place in the sky (overhead for example), this is what people usually think of as a 'day' and is what our clocks measure.  For this way of defining the length of a day there are exactly 24 hours in a day, and in scientific terms this is called a 'solar day'.
The other way of thinking about the length of a day is the time it takes for the Earth to rotate once about it's axis.  This is slightly shorter at only 23 hours 56 minutes and 4 seconds and is called a 'sidereal day'.

You can see why there is a difference between the two in the diagram below (which I admit we borrowed from Wikipedia!).  As the Earth rotates it is also moving around the Sun, so if you are living where the little red arrow is on the diagram by the time the Earth has rotated once (the curved arrows next to Earth show the direction of rotation) it has also moved along its orbit from position 1 to position 2, and although the Sun was directly above the red arrow at position 1 it isn't quite overhead at position 2.  For the Sun to be directly overhead again you have to wait until the Earth has moved and rotated a little further, to position 3, so the usual way people think of a 'day' is slightly longer than the time it takes Earth to spin once.