Life could (or could have) travel from Venus to Earth

Impact craters on the surface of Venus (image reconstructed from radar data)

So claims this article here on space.com.

It always baffles us proponents of more exploration of Venus that almost no effort is being made to check the cloudtops of Venus for life, along with Mars. These clouds are perfect environments for microbial life, Venus is that much easier to reach than Mars, and we can send a solar flyer there to check out the environment for a full 24 hours a day due to the slow rotation. As the article says:

The clouds on Venus are thought to be the planet's best bet for life because the temperatures there are cooler than at the too-hot surface, and water vapor has been detected in the atmosphere.

"The temperature and pressure there are entirely congenial to the survival of certain types of microbes," said researcher Chandra Wickramasinghe of the Cardiff Centre for Astrobiology at Cardiff University in Wales. "Microbes are known to survive in similar environments on Earth."

In particular, bacteria that have been found in extreme conditions in sulfurous hot springs on Earth would also thrive in the Venusian clouds, he said.

The premise of the article is that solar wind could transfer life from one planet to the other due to them being so close:

Venus, with its boiling-hot surface, doesn't seem a likely place to find ET. But a new paper argues not only that Venusian clouds could harbor microbial life, but also that the life there could potentially hitch a ride aboard the solar wind to Earth. The possibility for microbial life on Venusian clouds has been suggested before, though it's still not widely thought to be likely. However, the assertion that this life could potentially float from Venus to Earth is novel, and contentious.

The best time for this to happen is during the alignments of Earth and Venus:

"We point out that Venus and Earth are very close in terms of proximity," Chandra Wickramasinghe told SPACE.com. "There are occasions where Venus and Earth are aligned, which would be the best possible time for any exchange of material from Venus to Earth."

The last such alignment took place in 2004 and the next will happen in 2012, he said.

These take place in a pattern that repeats as follows (from Wikipedia):

Transits of Venus are among the rarest of predictable astronomical phenomena and currently occur in a pattern that repeats every 243 years, with pairs of transits eight years apart separated by long gaps of 121.5 years and 105.5 years. Before 2004, the last pair of transits were in December 1874 and December 1882. The first of a pair of transits of Venus in the beginning of the 21st century took place on June 8, 2004 (see Transit of Venus, 2004) and the next will be on June 6, 2012 (see Transit of Venus, 2012). After 2012, the next transits of Venus will be in December 2117 and December 2125.

So no more transits after 2012 for the living. These transits are particularly interesting because not only do they help to learn about Venus' atmosphere but they also help us in our search for extrasolar planets, especially the ones we're most interested in finding (the ones about our size):

There was however a good deal of interest in the 2004 transit as scientists attempted to measure the pattern of light dimming as Venus blocked out some of the Sun's light, in order to refine techniques that they hope to use in searching for extrasolar planets. Current methods of looking for planets orbiting other stars only work for a few cases: planets that are very large (Jupiter-like, not Earth-like), whose gravity is strong enough to wobble the star sufficiently for us to detect changes in proper motion or Doppler shift changes in radial velocity, Jupiter or Neptune sized planets very close to their parent star, or through gravitational microlensing by planets which pass in front of background stars with the planet-parent star separation comparable to the Einstein ring. Measuring light intensity during the course of a transit, as the planet blocks out some of the light, is potentially much more sensitive, and might be used to find smaller planets. However, extremely precise measurement is needed: for example, the transit of Venus causes the Sun's light to drop by a mere 0.001 magnitude, and the dimming produced by small extrasolar planets will be similarly tiny.

It's also possible that Venus could have had life a long time ago, even intelligent life. The geological surface is so young that anything over a billion years or so has been completely wiped out:

It is also noteworthy that there are a surprisingly low number of impact craters. This demonstrates that the surface is relatively young, approximately half a billion years old.

and:

Studies have suggested that several billion years ago Venus's atmosphere was much more like Earth's than it is now, and that there were probably substantial quantities of liquid water on the surface, but a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere.

So anything that was on Venus a billion or two years ago when the atmosphere was more like ours has been completely wiped out; nobody knows what was there.

Conclusion? Venus is much too interesting a planet to keep ignoring like this. We need solar flyers there as soon as possible.