We currently have no scientific evidence¹ of any form of life existing—past or present—anywhere in our universe besides Earth. 

Generally, our inability to traverse the vast immensity of our universe has limited our search for extraterrestrial life.

But it has become increasingly apparent in recent years that the number of habitable planets in the universe is also vast.

Astronomers estimate that there are about 400 billion stars in the Milky Way², our home galaxy. Our Sun, which is responsible for all life on Earth, is just one of these stars.

If we assume our planetary system to be of average size, this means there are potentially trillions of planets in our galaxy alone.

In our solar system, ⅛ of the planets currently have the right conditions to harbor life.

So even if just 1 in 1,000,000 of our galaxy's planets had the right conditions for life to exist, this would mean there could still exist millions of planets suitable to harbor life.

And that's just in our galaxy, which is one of the billions in our observable universe.

Keep in mind that this is not including dwarf planets or moons, which could provide exponentially more locations for life to exist. (There are over 200 moons in our solar system alone.)

Furthermore, since we only have Earthly examples to form our idea of "life" (plants, animals, microbes, etc.), who's to say life can't exist in another, previously unimaginable form?

Maybe there exist lifeforms which don't require things like sunlight, oxygen, liquid water, 4 dimensional spacetime, etc.

It's safe to say that the universe could be fertile with life, and that evidence of an extraterrestrial life form could be discovered at any moment—if it hasn't already.

¹ Anecdotes, UFO sightings, Ancient Aliens™, et al. are not considered evidence.

² Source: exoplanets.nasa.gov

³ Contest rules:
For the sake of this contest, "Extraterrestrial Life" is defined as any entity that meets all of the following requirements:

1. It must have biological [self-sustaining] processes (or evidence that it once did if found non-living).
2. It must occur, or have originated, somewhere other than Earth.

"Life" can include everything from known, Earth-like forms to non-cellular, unintelligent microorganisms, or even advanced, unimaginable forms of life. For this contest, viruses are not considered life.

In the event of any ambiguity, Stemcell Science Shop will have the final decision on the outcome of the contest.

Proof can be in any form but must be definitive and scientifically accepted.

The winning date will be the date of discovery—not the date of announcement, if different. In the event that the International Date Line lies between the discoverer and the contestant at the moment of discovery, the correct date will be that of the location of the discovery, if applicable.

For the sake of fairness, we will not consider entries placed on the day of announcement.

A prize of US$1,000 will be split among anyone who chose the correct date. If no one chose the correct date, US$500 will be split among those who chose the nearest future and past date.

If Stemcell Science Shop, the US dollar, currency, civilization, the Internet, or other integral components of the contest no longer exist upon the date of discovery, there will be no prize :(

These rules also apply in the event that evidence proves extraterrestrial life was definitively discovered at some point in the past (before this contest began).

If you don't believe life exists anywhere other than Earth, or that we'll ever find any, then simply ignore this survey altogether.

You can select any date between year 0 and 9999. This 10,000-year range is only a blink in cosmic time, but we don't plan to exist beyond 9999, so it doesn't matter.