What evidence is there to suggest there may be life on other planets?

Answer 1

We infer that living things use energy and need to replace it so some sort of nourishment is essential. We infer that some ability to move is necessary. Since living things are likely to have limited life spans (nothing lives forever) reproduction is necessary to continue the species. Over time some species are likely to disappear and new one appear-what we call evolution.

Our own planet has seen at least five major extinctions of life where most species died out-the dinosaur extinction is the most famous but not the only one. We don't know the reasons for these extinctions although impacts with large asteroids is believed to be the most likely reason.

We infer that living things exist within limits of temperature. Without our atmosphere, solar radiation would fry all earthly life exposed to it and all stars radiate so other planets would have atmospheres that protect life from being incinerated by radiation.

All the spaces in the Periodic Table of the Elements that represent stable elements are occupied. Therefore although unknown compounds may exist elsewhere, there won't be any unknown stable elements. Oxygen and carbon are present in every life form on Earth.

Answer 2

There are many different factors that are critical for life to exist on any planet.

Some of these are:

1 Must be a spiral galaxy, most galaxies in the universe are not spiral galaxies.

2 Must be in the habitable zone within that galaxy

3 Must orbit a star of the right mass and luminosity.

4 Solar system Must have larger planets like Uranus, Jupiter that can block comets / asteroids

5 Must be within the habitable zone of that solar system

6 Must have a large moon to stabilize planet wobble

7 Must be a terrestrial planet, not a gas planet like Jupiter.

8 Must have large oceans

9 Must have a thin enough crust for plate tectonics

10 Must have a molten iron core to establish magnetic field

11 Clear oxygen rich atmosphere

Answer 3

None, so far - except for theoretical considerations:

1. The sheer number of planets makes it likely that at least some of them would harbor life.

2. Even on Earth, some creatures (notably Archaea) have managed to live, even thrive, under quite extreme conditions, so the extreme conditions on other planets might not always be a hindrance for the development of life. On the other hand, we know fairly little, especially about the first stages of how life developed, so it is really hard to tell for sure.

None, so far - except for theoretical considerations:

1. The sheer number of planets makes it likely that at least some of them would harbor life.

2. Even on Earth, some creatures (notably Archaea) have managed to live, even thrive, under quite extreme conditions, so the extreme conditions on other planets might not always be a hindrance for the development of life. On the other hand, we know fairly little, especially about the first stages of how life developed, so it is really hard to tell for sure.

None, so far - except for theoretical considerations:

1. The sheer number of planets makes it likely that at least some of them would harbor life.

2. Even on Earth, some creatures (notably Archaea) have managed to live, even thrive, under quite extreme conditions, so the extreme conditions on other planets might not always be a hindrance for the development of life. On the other hand, we know fairly little, especially about the first stages of how life developed, so it is really hard to tell for sure.

None, so far - except for theoretical considerations:

1. The sheer number of planets makes it likely that at least some of them would harbor life.

2. Even on Earth, some creatures (notably Archaea) have managed to live, even thrive, under quite extreme conditions, so the extreme conditions on other planets might not always be a hindrance for the development of life. On the other hand, we know fairly little, especially about the first stages of how life developed, so it is really hard to tell for sure.

Answer 4

An atmosphere and liquid surface water are the primary ingredients for life as we know it. On earth multicellular life first originated in our oceans, and most life on earth exists there today. That would likely be the case with extraterrestrial life.

All earth life consists of carbon, hydrogen, oxygen, nitrogen, sulfur, and trace amounts of other elements. These would likely constitute the primary ingredients of life anywhere.

Answer 5

None, so far - except for theoretical considerations:

1. The sheer number of planets makes it likely that at least some of them would harbor life.

2. Even on Earth, some creatures (notably Archaea) have managed to live, even thrive, under quite extreme conditions, so the extreme conditions on other planets might not always be a hindrance for the development of life. On the other hand, we know fairly little, especially about the first stages of how life developed, so it is really hard to tell for sure.

Answer 6

That is not currently known with any large degree of certainty - we know for certainty about life on one single planet.Among other things, it is often assumed that a planet needs to have a certain temperature range, as well as water, to be able to harbor life; however:

* This doesn't guarantee that life will actually have evolved on such a planet.

* Life may well be able to evolve under more extreme circumstances.

Answer 7

Scientists will typically look for evidence of water. Water can have a whole host of different microscopic plants and molecules.

Answer 8

Changes in/on the planet that cannot be explained by chemistry or physics but must come from Biology: things that grow and change during time periods of days or weeks.

Answer 9

Because we can't be sure there isn't someone out there watching us . .