Q: Could Mars be made suitable for human life by raising plants to produce oxygen?

Plants are indeed part of one theoretical plan for turning Mars into a suitable environment for human beings, a process called terraforming. Raising plants is not the initial step, but would come very late in the game, probably after centuries of climate change.

Chris McKay, a Mars expert at the NASA Ames Research Center, theorizes that engineers would first have to encourage the kind of global warming they want to avoid on Earth. This could be done by releasing greenhouse gases, like chlorofluorocarbons or perfluorocarbons, into the atmosphere. The goal would be to increase the surface temperature of Mars by a total of about 7.2 degrees Fahrenheit.

The gases would be produced on the planet by processing chemicals from its atmosphere and soil in giant factories. With the rise in temperature, heat-trapping carbon dioxide would eventually be released from the planet’s south polar ice cap, producing a further average temperature rise of perhaps as much as 126 degrees Fahrenheit.

These high temperatures would melt ice to produce the water needed for living things. Only then would trees be planted to absorb carbon dioxide and produce enough oxygen for humans.

Q: Do many germs escape into the air when a toilet is flushed, and do they affect our health?

The jury is still out on this age-old question, a new review of the scientific literature suggests.

The possible peril of a toilet plume became famous through a 1975 study by Charles Gerba in the journal Applied Microbiology. Gerba seeded household toilets with disease germs and then tested to see if they survived after flushing. He concluded that “there is a possibility that a person may acquire an infection from an aerosol produced by a toilet.”

But a new review article finds that there are, as yet, no direct cases of proven infection, and that the possible risk is still unknown. The researchers looked at all the peer-reviewed studies of the matter, both epidemiological and microbiological. Their study, published last month by The American Journal of Infection Control, says that “no studies have yet clearly demonstrated or refuted toilet-plume-related disease transmission, and the significance of the risk remains largely uncharacterized.”

The new study concludes that toilet plumes “could play a contributory role in the transmission of infectious diseases” but that additional research is warranted to assess the risks.