All the scientific reasons aliens exist

This is not some conspiracy theory... plausible, logical scientific evidence for extraterrestrial life. All in one place.

Features on Mars match features caused by microbes on earth
A careful study of images taken by the NASA rover Curiosity has revealed intriguing similarities between ancient sedimentary rocks on Mars and structures shaped by microbes on Earth. The findings suggest, but do not prove, that life may have existed earlier on the Red Planet.
In a paper published online last month in the journal Astrobiology (the print version comes out this week), Noffke details the striking morphological similarities between Martian sedimentary structures in the Gillespie Lake outcrop (which is at most 3.7 billion years old) and microbial structures on Earth.

Complexity of life on a graph falls in line... a line that shows life originated before earth

As life has evolved, its complexity has increased exponentially, just like Moore’s law. Now geneticists have extrapolated this trend backwards and found that by this measure, life is older than the Earth itself.

Space is full of dormant bacteria waiting to be seeded on a planet
cosmic dust particles are of exactly the right sizes to be identified with microorganisms 

Space dust and dormant bacteria match up in spectral analysis and sizes on the nanometer scale
But Hoyle and Wickramasinghe were not satisfied. In the middle 1970s, they turned their attention to an apparent anomaly in the spectrum. It had a low, broad "knee" centered at about 2.3 wavelengths per micrometer (the slight convexity on the slope at the left side of the graph above) (9). This spectral feature could be explained if the grains of dust were of a certain size, and translucent. After trying almost everything else first, in 1979, they looked at the spectrum for bacteria. Dried bacteria refract light as irregular hollow spheres, and their size range is appropriate. The match between the spectrum for dried bacteria (solid line) and the ones from the interstellar grains (dots, triangles and squares) was nearly perfect. Thinking without prejudice, Hoyle and Wickramasinghe concluded the grains probably were dried, frozen bacteria.
The early universe had conditions that were very hospitable to life
In the redshift range 100<(1+z)<137, the cosmic microwave background (CMB) had a temperature of 273-373K (0-100 degrees Celsius), allowing early rocky planets (if any existed) to have liquid water chemistry on their surface and be habitable, irrespective of their distance from a star. In the standard LCDM cosmology, the first star-forming halos within our Hubble volume started collapsing at these redshifts, allowing the chemistry of life to possibly begin when the Universe was merely 10-17 million years old.
 Meteorites are evidence that DNA was made in space
"People have been discovering components of DNA in meteorites since the 1960's, but researchers were unsure whether they were really created in space or if instead they came from contamination by terrestrial life," said Dr. Michael Callahan of NASA's Goddard Space Flight Center, Greenbelt, Md. "For the first time, we have three lines of evidence that together give us confidence these DNA building blocks actually were created in space."  
This is straight up. ISRO finds life in space. 
In a major scientific breakthrough Indian Space Research Organisation (ISRO) claims to have found three unknown species of bacteria about 40 kilometres above the earth's surface.  
What if we are the exception, and there are planets where the environment is actually more conducive to life?
To be habitable, a world (planet or moon) does not need to be located in the stellar habitable zone (HZ), and worlds in the HZ are not necessarily habitable. Here, we illustrate how tidal heating can render terrestrial or icy worlds habitable beyond the stellar HZ. Scientists have developed a language that neglects the possible existence of worlds that offer more benign environments to life than Earth does. We call these objects "superhabitable" and discuss in which contexts this term could be used, that is to say, which worlds tend to be more habitable than Earth.   
 Statistically, every star in the milky way is likely to have earth like planets in the habitable zone
We analyze a sample of multiple-exoplanet systems which contain at least 3 transiting planets detected by the Kepler mission ("Kepler multiples"). We use a generalized Titius-Bode relation to predict the periods of 228 additional planets in 151 of these Kepler multiples. These Titius-Bode-based predictions suggest that there are, on average, ~2 planets in the habitable zone of each star. 
 The chemistry required for life formation can occur in deeps space, not necessarily in an organic soup on an earth like planet in a habitable zone 
“It is fascinating to consider that the most basic biochemical building blocks that led to life on Earth may well have had an extraterrestrial origin,” said UC Berkeley chemist Richard Mathies, coauthor of a paper published online last week and scheduled for the March 10 print issue of The Astrophysical Journal.
Russians cleaning up the ISS came across Marine Plankton
The results of the recent experiments prove that that some organisms are capable of living on the outer surface of the International Space Station (ISS), Vladimir Solovyev, head of the Russian segment of the ISS, has revealed. Some studies suggest that these organisms may even develop in the hostile conditions of spaceflight, which include vacuum, low temperatures, radiation and others, he added. “The results of the so-called ‘Test’ experiment are unique. On the surface of the [ISS] windows we found traces of marine plankton – the microparticles – that will become the subject of further studies,” Solovyev was quoted as saying by Itar-Tass.
Now there are a bunch of organic molecules found in space.
iso-propyl cyanide
amino acids 
and lots of alcohol 
Organic molecules were also found on Philae.