I get really excited over exoplanets that are Earth-like so I’m wondering how this works.
In: Planetary Science
“Maybe”.
That’s about all there is to it. ;p
Yes, if something is XXX light-years away, we can only see what it was like XXX years ago.
Not necessarily, if the exoplanet has the correct circumstances.
For example, there are organism here on Earth who live deep down in the ocean by geothermic vents, basically small underwater volcanoes.
If the planet in question has enough geothermic activity and water to sustain these kinds of conditions, then there’s the chance that the planet can sustain some form of life.
This is only purely speculative however, since we don’t really know exactly what is required for life to form and be sustained, but I’d say it’s not impossible to imagine a planet which can be self-sustaining to at least some extent, however unlikely.
Will it be very earth-like though? No, probably not.
There are some stars that have been detected that are so far away that they will have died billions of years ago.
Known exoplanets on the other hand are around stars that are much closer. If an exoplanet is detected around a star that is a few thousand light years away then they are almost certainly still around. Thousands of years isn’t very long in the lifetime of stars so odds are that those stars and their exoplanets are alive and doing fine.
Define “dead.”
Stars don’t really die. They change form. Sometimes they explode, but then might form into new stars billions of years later.
The planets around them may or may not still be there.
If you mean dead as in can’t support life, that’s most exoplanets already. But when a star changes or explodes, it won’t be more productive for life, so that would make the planet “deader.”
So “dead” is a term that will probably confuse your understanding of exoplanets because planets themselves are not alive.
Most of the exoplanets we find, we can see them because they are around active stars and they affect the star, or the light from the star, in some way.
We think that for life to be on exoplanets, one of the (many) conditions is that they need to be orbiting an active star. So most of the exoplanets we find pass this criteria. That said we also look for planets similar in size to earth, and that are a distance from the star that is not too cold or not too hot (the Goldilocks or habitable zone).
So while we’ve found over 5,000 exoplanets, less than 5 are earth size and in the stars habitable zone.
“Dead” has different meanings when talking about “dead stars” and “dead planets”. Dead planets are those planets which cannot sustain life – but I think you already understand this, as you mentioned Earth-like exoplanets.
A dead star, on the other hand, has nothing to do with sustaining life. It is a star that has burnt through its supply of fuel. Like our sun, all stars burn hydrogen – but when that runs out, the star swells and collapses in on itself, before exploding in one final, bright burst, called a supernova. This then collapses, leaving either a neutron star (the remnants of the dead star, compressed into a very small package), or – if the star was very big – a black hole.
So, why can we still see some dead stars today? Because the light from those stars has to travel vast distances across space to reach us. Light travels at just under 300,000 km per second – but those distances in space between stars and us are much, much greater. The distance light travels in one Earth year (a “light year”) is about 9.461 trillion km. The nearest star to us (apart from the sun) – Proxima centauri – is about 4.25 light years away. The light from our *nearest* star takes 4.25 years to reach us. Most of the stars we can see are tens or hundreds of light years away.
So, let’s say there’s a star in the sky that died 100 years ago, and let’s say that star is (was) 150 light years away from us. When we see that star in the sky, we are seeing that star 150 years ago. Even though that star died 100 years ago, we will still see it in the sky until the last of its light reaches us, in another 50 years.
All undisputed exoplanet discoveries are in our own galaxy, most of them within a few thousand light years, and most of them around stars that are somewhere in the middle of their multi-billion-year life. We have found ~5000 exoplanets so far. It’s likely all of them still exist with essentially unchanged stars.
Kinda depends. Keep in mind stars are really big and really bright, therefore we can see them from really far away. The exoplanets we can see are much much smaller so they are much closer than the dead stars we can see. As a result, we know how far back in time we’re seeing them and can make an educated guess on if they’re “dead” or not. Obvious we don’t know if they actually contain life or if they have an intact atmosphere. But we know what kind of a sun they have. The life cycles of a star a measured in billions of years so if it’s 5,000 light years away, we’re basically seeing it in real-time relative to that sort of scale of time.
Planets are not alive as far as we know.
Are you asking if they’ve been destroyed?
Possibly, but not necessarily.
Not really.
People hear that stars are a very long way away and that the light that reaches us from them is also very old, but they don’t really have a sense of scale about how far and how long those distances and times are.
The most distant exo-planet discovered is 17,000 light years away.
Most that we have found are much closer.
The time delay when observing exo planets varies from as far back as us starting to figure out agriculture in earnest to hording toilet paper while isolating from covid-19.
The shortest lived stars are very rare blue super giants which last for 10 million years.
Our own sun is 5 billion years old and will last for maybe 9 or 10 more billion years.
Red dwarfs, which are the most common type of star can last for trillions of years.
So yes, in theory it is possible that some of the planets that we have found have been long gone, but only in the same way that a toddler without object permanence fearing that their parents have ceased to exist while they are briefly out of view is partially justified in their fears.
Planets and star last a long time and a few years or centuries or even millennia lag while observing them does not matter much.
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