If intelligent, technological extraterrestrial life exists in the galaxy, then it is conceivable that such a civilization might embark on a similar exploration strategy. Extraterrestrial intelligent (ETI) civilizations may choose to pursue astronomy and search for planets orbiting other star systems and may also choose to follow-up on some of these targets by deploying their own remote exploratory spacecraft. If nearby ETI have observed the Solar System and decided to pursue further exploration, then evidence of ETI technology may be present in the form of such exploratory probes. We refer to this ETI technology as “non-terrestrial artifacts”, in part to distinguish these plausible exploratory spacecraft from the flying saucers of science fiction.

In a recent paper titled “On the likelihood of non-terrestrial artifacts in the Solar System”, published in the journal Acta Astronautica, myself and co-author Ravi Kopparapu discuss the likelihood that human exploration of the Solar System would have uncovered any non-terrestrial artifacts. Exploratory probes destined for another star system are likely to be relatively small (less than ten meters in diameter), so any non-terrestrial artifacts present in the Solar System have probably remained undetected. The surface and atmosphere of Earth are probably the most comprehensively searched volumes in the Solar System and can probably be considered absent of non-terrestrial artifacts. Likewise, the surface of the moon and portions of Mars have been searched at a sufficient resolution to have uncovered any non-terrestrial artifacts that could have been present. However, the deep oceans of Earth and the subsurface of the Moon are largely unexplored territory, while regions such as the asteroid belt, the Kuiper belt, and stable orbits around other Solar System planets could also contain non-terrestrial artifacts that have so far escaped human observation. Because of this plenitude of nearby unexplored territory, it would be premature to conclude that the Solar System is absent of non-terrestrial artifacts.

Although the chances of finding non-terrestrial artifacts might be low, the discovery of ETI technology, even if broken and non-functioning, would provide evidence that ETI exist elsewhere in the galaxy and have a profound impact on humankind. We do not argue that the search for non-terrestrial technology should be given priority over other astronomical missions; however, as human exploration into the Solar System continues, we may as well keep our eyes open for ETI technology, just in case.

In a recent paper published in Nature Geoscience, on which I am a co-author, we examine the idea that early Mars featured a cold glacial ocean on its northern hemisphere. This study combines some theoretical climate calculations (which was my contribution) along with a mineralogical analysis to reach this conclusion. In particular, the formation of minerals known as phyllosilicates would have been prevented in a cold ocean, which may explain the scarcity of phyllosilicates observed in the northern martian hemisphere today.

And if oceans did exist on Mars billions of years ago, then perhaps the processes of life also could have arisen in the early history of the red planet. Mars today appears barren and lifeless, but signs of past or present life could very well be lurking beneath the soil. Future Mars missions, and possibly human exploration, will eventually help to uncover this mystery.

In a recent paper published in the journal Space Policy, my co-authors Dimitra Atri and Julia DeMarines and I propose the development of a METI protocol in order to guide the construction and transmission of messages to extraterrestrials. A METI protocol would include technical considerations such as the method of signal encoding, message length, and transmission strategy. This protocol would also provide guidelines for the content of messages, which includes limits on culturally-dependent, anthropocentric, or sense-dependent information. This will help ensure that a message into space is more representative of Earth as a whole and may also increase the likelihood that the message is understood by potential listeners.

As a way of testing messages and promoting educational outreach, we will implement an interactive website in which users can attempt to submit or decrypt messages according to a METI protocol. This will allow messages to be tested across cultural borders, which arguably is a minimum requirement for a message that would be sent to unknown extraterrestrial listeners. Such an exchange will also help users of the website to gain insight into cultures other than their own by discovering success or failure at effectively communicating a message to unknown receivers on Earth.

In a recent paper written by myself and my two graduate advisers, we argue that small quantities of O₂ could have reached the surface of early Earth through transport by atmospheric dynamics. This transport would primarily occur in the Wintertime hemisphere, where a “polar Winter vortex” develops near the polar region, because the lack of sunlight in Winter would allow for greatest amount of O₂ to accumulate. Our calculations show that enough dissolved O₂ could have accumulated in polar Winter waters to allow early forms of marine life (i.e. microbial life) to develop and use respiration–without needing to wait for photosynthesis to oxygenate the atmosphere. Although our model calculations cannot prove that respiration did in fact evolve first, they least demonstrate a proof-of-concept that the “early-respiration” hypothesis is in fact viable.

Our paper is titled “Availability of O₂ and H₂O₂ on pre-photosynthetic Earth” and appears in the May issue of the journal Astrobiology.

Many attempted resolutions have been proposed to this problem, but none has provided a complete solution for a warm, wet early Mars. In a recent paper published in Earth and Planetary Science Letters, on which I am a co-author, we argue that greenhouse warming by sulfur dioxide could not have kept early Mars warm enough. Sulfur dioxide has been suggested in the literature because it is an effective greenhouse gas, similar to carbon dioxide or methane. However, we show that atmospheric photochemistry with sulfur dioxide leads to the production of sulfate aerosols in the upper atmosphere that absorb incoming sunlight and cool the surface. Thus, sulfur dioxide may have caused net cooling on early Mars, rather than warming.

We’re still trying other mechanisms to explain a warm, wet early Mars. Most likely, it was some combination of processes, including several greenhouse gases and warming by clouds. A negative result for sulfur dioxide is not as exciting as a solution to the early Mars problem, but it’s still a small step forward.