According to widely-accepted theories, the Solar System formed roughly 4.6 billion years ago from a massive cloud of dust and gas (aka. Nebular Theory). This process began when the nebula experienced a gravitational collapse in the center that became our Sun. The remaining dust and gas formed a protoplanetary disk that (over time) accreted to form the planets.
However, scientists remain unsure about when organic molecules first appeared in our Solar System. Luckily, a new study by an international team of astronomers may be able to help answer that question. Using the Atacama Large Millimeter-submillimeter Array (ALMA), the team detected complex organic molecules around the young star V883 Ori, which could someday lead to the emergence of life in that system.
On July 14th, 2015, theNew Horizons mission made history when it became the first robotic spacecraft to conduct a flyby of Pluto. On December 31st, 2018, it made history again by being the first spacecraft to rendezvous with a Kuiper Belt Object (KBO) – Ultima Thule (2014 MU69). In addition, the Voyager 2probe recently joined its sister probe (Voyager 1) in interstellar space.
Given these accomplishments, it is understandable that proposals for interstellar missions are once again being considered. But what would such a mission entail, and is it even worth it? Kelvin F. Long, the co-founder of the Initiative for Interstellar Studies (i4iS) and a major proponent of interstellar flight, recently published a paper that supports the idea of sending robotic missions to nearby star systems to conduct in-situ reconnaissance.
In their efforts to find evidence of life beyond our Solar System, scientists are forced to take what is known as the “low-hanging fruit” approach. Basically, this comes down to determining if planets could be “potentially habitable” based on whether or not they would be warm enough to have liquid water on their surfaces and dense atmospheres with enough oxygen.
This is a consequence of the fact that existing methods for examining distant planets are largely indirect and that Earth is only one planet we know of that is capable of supporting life. But what if planets that have plenty of oxygen are not guaranteed to produce life? According to a new study by a team from Johns Hopkins University, this may very well be the case.
On October 19th, 2017, the first interstellar object – named 1I/2017 U1 (aka. ‘Oumuamua) – to be observed in our Solar System was detected. In the months that followed, multiple follow-up observations were conducted to gather more data on its composition, shape, and possible origins. Rather than dispel the mystery surrounding the true nature of ‘Oumuamua – is a comet or an asteroid? – these efforts have only managed to deepen it.
In a recent study, Harvard Professor Abraham Loeb and Shmuel Bialy – a postdoctoral researcher from the Smithsonian Center for Astrophysics (CfA) – addressed this mystery by suggesting that ‘Oumuamua may be an extra-terrestrial solar sail. Building on this, Loeb and Amir Siraj (a Harvard undergraduate student) conducted a new study that indicated that hundreds of “‘Oumuamua-like” objects could be detectable in our Solar System.
Ever since the Pioneer and Voyager probes passed through the Jovian system in the 1970s, NASA and other space agencies have dreamed of one-day sending a mission to Europa. Beyond Earth, it is considered one of the most promising candidates for finding life, which could exist in the subsurface ocean that lies beneath the moon’s icy crust.
One of these concepts is known as the Cool High Impact Method for Exploring Down into Europan Subsurface (ARCHIMEDES), a proposed direct-laser penetrator that will use a laser light carried by an optical fiber tether to penetrate Europa’s icy crust. This mission could provide future missions with access to the ocean that exists beneath Europa’s surface and enable the search for life there.
When it comes to the search for extra-terrestrial life, scientists have a tendency to be a bit geocentric – i.e. they look for planets that resemble our own. This is understandable, seeing as how Earth is the only planet that we know of that supports life. As result, those searching for extra-terrestrial life have been looking for planets that are terrestrial (rocky) in nature, orbit within their stars habitable zones, and have enough water on their surfaces.
In the course of discovering several thousand exoplanets, scientists have found that many may in fact be “water worlds” (planets where up to 50% of their mass is water). This naturally raises some questions, like how much water is too much, and could too much land be a problem as well? To address these, a pair of researchers from the Harvard Smithsonian Center for Astrophysics (CfA) conducted a study to determine how the ratio between water and land masses can contribute to life.
Interestingly enough, there has also been some speculation that based on its shape, ‘Oumuamua might actually be an interstellar spacecraft (Breakthrough Listen even monitored it for signs of radio signals!). A new study by a pair of astronomers from the Harvard Smithsonian Center for Astrophysics (CfA) has taken it a step further, suggesting that ‘Oumuamua may actually be a light sail of extra-terrestrial origin.
The possibility that life could exist on Mars has captured the imagination of researchers, scientists and writers for over a century. Ever since Giovanni Schiaparelli (and later, Percival Lowell) spotted what they believed were “Martian Canals” in the 19th century, humans have dreamed of one day sending emissaries to the Red Planet in the hopes of finding a civilization and meeting the native Martians.
While the Mariner and Viking programs of the 1960s and 70s shattered the notion of a Martian civilization, multiple lines of evidence have since emerged that indicate how life could have once existed on Mars. Thanks to a new study, which indicates that Mars may have enough oxygen gas locked away beneath its surface to support aerobic organisms, the theory that life could still exist there has been given another boost.
In recent years, the number of confirmed extra-solar planets has risen exponentially. As of the penning of the article, a total of 3,777 exoplanets have been confirmed in 2,817 star systems, with an additional 2,737 candidates awaiting confirmation. What’s more, the number of terrestrial (i.e. rocky) planets has increased steadily, increasing the likelihood that astronomers will find evidence of life beyond our Solar System.
Unfortunately, the technology does not yet exist to explore these planets directly. As a result, scientists are forced to look for what are known as “biosignatures”, a chemical or element that is associated with the existence of past or present life. According to a new study by an international team of researchers, one way to look for these signatures would be to examine material ejected from the surface of exoplanets during an impact event.
As they indicate in their study, most efforts to characterize exoplanet biospheres have focused on the planets’ atmospheres. This consists of looking for evidence of gases that are associated with life here on Earth – e.g. carbon dioxide, nitrogen, etc. – as well as water. As Cataldi told Universe Today via email:
“We know from Earth that life can have a strong impact on the composition of the atmosphere. For example, all the oxygen in our atmosphere is of biological origin. Also, oxygen and methane are strongly out of chemical equilibrium because of the presence of life. Currently, it is not yet possible to study the atmospheric composition of Earth-like exoplanets, however, such a measurement is expected to become possible in the foreseeable future. Thus, atmospheric biosignatures are the most promising way to search for extraterrestrial life.”
However, Cataldi and his colleagues considered the possibility of characterizing a planet’s habitability by looking for signs of impacts and examining the ejecta. One of the benefits of this approach is that ejecta escapes lower gravity bodies, such as rocky planets and moons, with the greatest ease. The atmospheres of these types of bodies are also very difficult to characterize, so this method would allow for characterizations that would not otherwise be possible.
And as Cataldi indicated, it would also be complimentary to the atmospheric approach in a number of ways:
“First, the smaller the exoplanet, the more difficult it is to study its atmosphere. On the contrary, smaller exoplanets produce larger amounts of escaping ejecta because their surface gravity is lower, making ejecta from smaller exoplanet easier to detect. Second, when thinking about biosignatures in impact ejecta, we think primarily of certain minerals. This is because life can influence the mineralogy of a planet either indirectly (e.g. by changing the composition of the atmosphere and thus allowing new minerals to form) or directly (by producing minerals, e.g. skeletons). Impact ejecta would thus allow us to study a different sort of biosignature, complementary to atmospheric signatures.”
Another benefit to this method is the fact that it takes advantage of existing studies that have examined the impacts of collisions between astronomical objects. For instance, multiple studies have been conducted that have attempted to place constraints on the giant impact that is believed to have formed the Earth-Moon system 4.5 billion years ago (aka. the Giant Impact Hypothesis).
While such giant collisions are thought to have been common during the final stage of terrestrial planet formation (lasting for approximately 100 million years), the team focused on impacts of asteroidal or cometary bodies, which are believed to occur over the entire lifetime of an exoplanetary system. Relying on these studies, Cataldi and his colleagues were able to create models for exoplanet ejecta.
As Cataldi explained, they used the results from the impact cratering literature to estimate the amount of ejecta created. To estimate the signal strength of circumstellar dust disks created by the ejecta, they used the results from debris disk (i.e. extrasolar analogues of the Solar System’s Main Asteroid Belt) literature. In the end, the results proved rather interesting:
“We found that an impact of a 20 km diameter body produces enough dust to be detectable with current telescopes (for comparison, the size of the impactor that killed the dinosaurs 65 million years ago is though to be around 10 km). However, studying the composition of the ejected dust (e.g. search for biosignatures) is not in the reach of current telescopes. In other words, with current telescopes, we could confirm the presence of ejected dust, but not study its composition.”
In short, studying material ejected from exoplanets is within our reach and the ability to study its composition someday will allow astronomers to be able to characterize the geology of an exoplanet – and thus place more accurate constraints on its potential habitability. At present, astronomers are forced to make educated guesses about a planet’s composition based on its apparent size and mass.
Unfortunately, a more detailed study that could determine the presence of biosignatures in ejecta is not currently possible, and will be very difficult for even next-generation telescopes like the James Webb Space Telescope (JWSB) or Darwin. In the meantime, the study of ejecta from exoplanets presents some very interesting possibilities when it comes to exoplanet studies and characterization. As Cataldi indicated:
“By studying the ejecta from an impact event, we could learn something about the geology and habitability of the exoplanet and potentially detect a biosphere. The method is the only way I know to access the subsurface of an exoplanet. In this sense, the impact can be seen as a drilling experiment provided by nature. Our study shows that dust produced in an impact event is in principle detectable, and future telescopes might be able to constrain the composition of the dust, and therefore the composition of the planet.”
In the coming decades, astronomers will be studying extra-solar planets with instruments of increasing sensitivity and power in the hopes of finding indications of life. Given time, searching for biosignatures in the debris around exoplanets created by asteroid impacts could be done in tandem with searchers for atmospheric biosignatures.
With these two methods combined, scientists will be able to say with greater certainty that distant planets are not only capable of supporting life, but are actively doing so!