If we detect a planet that's 450 lightyears from earth, can it no longer be there?

Question

I recently read a new planet was detected 450 lighyears, can it be possible that the planet doesn't exist anymore? and we are just detecting the light that was projected by it. If what we see is what light reflects then wouldn't scientist be detecting a planet that was there 450 years ago. In other words if someone is in that planet right now looking at earth, wouldn't that person be looking at the very past?

Answer 1

Yes, their astronomers (assuming they had some, perhaps on a terrestrial planet in the same system as the planet we have just discovered is, I believe, an inhospitable gas giant) would see the earth of 1556, with the first Elizabethan Age about to dawn in England (Elizabeth I came to the throne in 1558) though at their moment of viewing we are coming towards the end of the second one (Elizabeth II is now 80).

Yes, it is possible this planet is no longer there, today. But unlikely. It is possible that Proxima Centauri (the nearest star to us) has turned into a supernova in the last 4.22 years and we don't yet know that either. But unlikely. And possible that in the last three minutes the Sun has turned into a black hole and has already swallowed Mercury and is about to gobble up Venus. But unlikely.

I can say "unlikely" with some confidence because it would not fit with our current theories of how a supernova or a black hole happens.

Let us look at these in turn

SUPERNOVA:

A supernova (pl. supernovae) is a stellar explosion which produces an extremely bright object made of plasma that declines to invisibility over weeks or months.

There are several different types of supernovae and two possible routes to their formation. A massive star may cease to generate fusion energy from fusing the nuclei of atoms in its core, and collapse under the force of its own gravity to form a neutron star or black hole.

Alternatively, a white dwarf star may accumulate material from a companion star until it nears its Chandrasekhar limit and undergoes runaway nuclear fusion in its interior, completely disrupting it.

In either type of supernova, the resulting explosion expels much or all of the stellar material with great force.

So the issue is whether the parent star of the newly discovered planet is either a massive star (such as Betelgeuse in Orion is, but our sun is not) or one of a binary system, one member of which is a white dwarf on which material transfers from the larger star to the smaller one.

I take it the star we are talking about is HAT--P-1 reported on 14th September.
Distance 139 (± 20) parsecs (450 ± 65 light years)
Spectral Type GOV (a little brighter than our Sun which is G2V)
Apparent Magnitude = 10.4 (not visible to the naked eye)
Mass 1.12 (± 0.09) x the mass of our sun (a little larger than our sun)
Age 3.6 billion years (about 80% of the age of our sun)

So it is too small to go supernova and it will be some 5-6 billion years before it will become a white dwarf. And it doesn't have a companion star anyway (well, put it this way, one isn't mentioned)...

BLACK HOLES:

As stated above these only form when a star gravitationally collapses under its own weight.

It is thought there is a threshold for the mass required for this to be possible: a stellar remnant above about three to five times the mass of the Sun (the Tolman-Oppenheimer-Volkoff limit) would be unable to support itself as a neutron star via degeneracy pressure, and would inevitably collapse into a black hole.

Stellar remnants with this mass are expected to be produced immediately at the end of the lives of stars that are more than 25 to 50 times the mass of the Sun.

Stellar collapse will generate black holes containing at least three solar masses. Black holes smaller than this limit can only be created if their matter is subjected to sufficient pressure from some source other than self-gravitation.

So with a stellar mass in the range 1.04 to 1.21 Solar Masses, citizens of HAT--P-1's planet(s?) can sleep easily in their beds tonight. Their star is far too young and not heavy enough to be at risk of ending up as a Black Hole, now or later,

Answer 2

Yes of course since we are seeing it as it was 450 years ago, it could have disappeared in the meantime.

Now, 450 years is nothing in astronomical time - I mean it is very exceptional that anything big could happen over such a very short period.

And even though a planet is much smaller than a star, you still need some major disaster to make it disappear. Think of the Earth. To make it disappear, the best way would be a collision with a heavy object, heavy enough so the Earth gets slowed down massively on its orbit and starts falling towards the sun (an asteroid would be far from sufficient). But there aren't any such objects around. Only an another planet would work, but why would it leave its own orbit and hit us?

Or else you'd need to have some "wild" star happening to travel towards us and happening to hit the Earth. But with stars typically at least a few light-years away from each other, such a collision would be very, very, very unlikely.

And as for someone there looking at the Earth. Yes they would be seeing it as it was back in 1550 or so.

Hope this helps

Answer 3

We aren't actually detecting the light from the planet. Planets around other stars are found by detecting the movement of the star forward and back as the orbiting planet pulls it one way then another.
Still, what we detect IS 450 year old information. It is possible that the planet is no longer there but very unlikely in such a short time span. We'll know in 450 years :-)

Answer 4

Good Q. Universe was established long before we started to explore them. How can we see and feel the sun every day, though it is far far away? How can we keep seeing the stars every night? Bcuz they have long before, established thier "rays" on earth and it is constantly on earth, so the viewing is continous for our eyes. However, there is a good chance that we will be seeing the sun for next 350 light yrs even if it is to be destroyed today.

Hmm.. that gives me another question .. how can our scientists claim that there is/was a planet at some x,y,z position, 450 light years away from earth? I mean.. wouldnt it take 450 yrs to measure that distance? Or may be they do it by other means (measurement) and give the numbers in light years .. maybe they dont use light reflection theory.. or they simply goofing bcuz none can invalidate thier claim for an arbitary number :P not sure here.

Answer 5

Chances are it's still there, since 450 years is a very short time in space terms, but yes. It is entirely possible that planet may no longer exist.

Your analysis is exactly correct. If an astronomer on that planet was looking at the earth he'd be seeing the world of Martin Luther.

Answer 6

If there is some uncertainty about the distance of the star (450 ± 65 light years) then the events on earth they would be observing today could have taken place anywhere between 1491 and 1621

Answer 7

It is possible that the planet was destroyed 449 years, and 364 days ago. Yes... if they are looking at earth right now, then they are seeing what was happening 450 years ago here on Earth.

Answer 8

It's possible. I'm only sure that the Sun was there 8 1/3 minutes ago. The center of our galaxy is 35,000 light years away so if it exploded within the last 35,000 years we wouldn't know it yet. If you've ever done anything really embarassing, some alien might be seeing you do it in his telescope right now and laughing at you histerically.

Answer 9

Of course it's possible but in that short period of time not likely.....450 years isn't a blink of one's eye.
What we are seeing would be 450 years old but planets would usually still be there.
(but possibly it wouldn't, or would be extremely changed...not likely though)

Answer 10

Everything you said is true. To look into space is to look into the past, But really the odds of the planet not beeing there is remote.