A century ago, scientists ostracized a famous pioneering Arizona astronomer, Percival Lowell, for theorizing that features observed on the surface of Mars, including those he interpreted as canals, showed that Mars once sustained intelligent life.
Despite intense scrutiny by today's powerful advanced telescopes – most notably the Mars-orbiting High Resolution Imaging Science Experiment camera operated from The University of Arizona that could see a human standing on the Martian surface – there's still no evidence for advanced life forms on Mars.
But Lowell may have been right about there being life on Mars before there was life on Earth by a mechanism he didn't imagine, says University of Arizona Regents' Professor of planetary sciences H. Jay Melosh.
That mechanism is meteorites.
"The mechanism by which large impacts on Mars can launch boulder-sized surface rocks into space is now clear," said Melosh, who is considered one of the world's foremost experts on impact cratering and the importance of extraterrestrial impacts in shaping life on Earth.
"Both theory and direct measurements on some of these rocks tell us that living microbes could have survived both the launch and travel in the vacuum of space for periods long enough for them to have arrived intact on the surface of our planet," he said.
The reverse journey of surface rocks launched from Earth and landing on Mars is likewise possible, he added.
"Research at the UA and elsewhere has filled in many details of this process. Biological exchange between the planets of our solar system seem not only possible, but inevitable," Melosh said.
Although scientists yet lack proof that such an exchange has actually occurred, "we now know what to look for," he said.
Further discoveries could vindicate Percival Lowell's belief that there was life on Mars before there was life on Earth.
"Life could have originated on the planet Mars and then traveled to Earth," Melosh concludes.
He said, "In that case, we are, in fact, all Martians."
Melosh will deliver the Blitzer Award Lecture, "Are We All Martians? The Meteoritic Exchange of Life Between Planets," at 4 p.m. Wednesday, Feb. 25, in Room 201 of UA's Physics and Atmospheric Sciences building, 1118 E. 4th Street.
The talk, free and open to the public, will be followed by a reception in the PAS lobby.
Pay parking is available at the Sixth Street Parking Garage, 1201 East Sixth Street.
The Blitzer Award
The Leon and Pauline Blitzer Award for Excellence in the Teaching of Physics and Related Sciences is given to members of the UA physics, astronomy, atmospheric sciences and planetary sciences faculty.
The award is funded by an endowment set up by the children and friends of Leon and Pauline Blitzer, who were UA alumni, in 2005.
UA physics professor Ke Chiang 'Johnny' Hseih, associate professor of astronomy Michael Meyer, and atmospheric sciences professor emeritus E. Philip Krider previously received the award.
Leon Blitzer was a physics professor from 1946 until his retirement in 1985. His wife, Pauline Blitzer, whom he married in 1942, was a teacher and activist in civic and charitable organizations.
Leon Blitzer's research focused on spectroscopy, astrophysics and celestial mechanics. In 1952 he received one of the first grants in the department's history, in the amount $12,000 from the Office of Ordnance Research.
He became the youngest full professor on campus at the age of 33 and was devoted to teaching, both graduate and undergraduate levels.
Pauline Blitzer received a bachelor's degree in education in 1940 and taught elementary school in California and in Tucson until she retired in the early 1950s.
She actively raised funds for a teaching hospital in Israel, civil rights groups and for organizations that fought cystic fibrosis and heart disease.