Making humans an interstellar species is an ambitious dream carried by many scientists (including the late Stephen Hawking), science fiction writers and enthusiasts. But before that, we must design and test means of propulsion and interstellar transport that would allow us to reach the nearest star in a reasonable time. In this ambition, researchers motivated by the Starlight project of NASA - aiming to send space sails propelled by laser beams - are studying which species it would be possible to place on board the first interstellar vessels. And, you may have guessed it, the tardigrades are among the finalists.
In a new study entitled "Interstellar space biology via Project Starlight", published in the journal Acta Astronautica, an international team of researchers determines which animal species would be the most suitable to embark on an interstellar journey, which should last about twenty years, aboard the first (tiny) sailing vessels.
The DEEP IN (Directed Energy Propulsion for Interstellar Exploration) system, proposed by NASA as part of the Starlight project, aims to propel space sails at at least 20% of the speed of light using laser beams pointed from Earth. Thus, it would be possible to reach the nearest star and planetary system, Alpha Centauri (located 4.367 light years away), in just over 20 years.
To infinity and beyond
The researchers thus selected species known for their resistance to different extreme environments, including nematodes, rotifers, fungi, bacteria and of course, tardigrades. As some of you know, tardigrades already know space: study projects aboard the International Space Station, for example, have shown that they are able to survive the vacuum of space. More recently, an Israeli lunar mission took thousands of tardigrades aboard a probe which unfortunately crashed. Yes, at the present time, it is therefore likely that thousands of water bears (as they are sometimes nicknamed) are "quietly" wandering around the surface of the Moon.
In other words, these incredible animals, measuring only 0.5 millimeters in length and whose biology is still partially understood, are already true explorers of space. Without exaggerating, they are some of the most resilient animals that we know of. So, there is no doubt: among the first earthly interstellar travelers there will be tardigrades.
Where are we in terms of galaxy exploration?
So far, only five ships have left our solar system. These ships, of which the two Voyager probes are a part, take decades just to leave our system and reach interstellar space, the limit of which is about 18 billion kilometers from Earth.
This same distance could be covered in just a few days by NASA's solar sails, and thus allow us to test the feasibility of transporting the first forms of life over such great distances. Previous long-range ships only contained messages, such as the etched gold discs of Voyager probes. “As directed energy propulsion capabilities develop, relativistic flight will become possible,” the researchers write in their study.
Take inspiration from tardigrades to make humans resistant to space travel
In a new study, Stephen Lantin of the University of Florida and his colleagues analyzed the amount of food needed to keep different species alive, their weight, and their resistance to radiation levels and the strong accelerations they would encounter during their trip. And the tardigrades, requiring little maintenance, appear to be excellent candidates to become the first interstellar travelers.
“It would be nice to send humans, but there are some biological constraints that would make it more favorable for us to send other organisms, at least during the first flights,” Lantin says. "It takes a lot of energy to send anything into interstellar space, at least at the speeds we are proposing, and to do that requires a really small payload." Unfortunately, such a flight would be a mission of no return.
Tardigrades and the tiny Caenorhabditis elegans , a nematode species included in the study, both have the advantage of being capable of cryptobiosis, a form of extreme hibernation in which animals drastically slow their metabolism when they are under adverse conditions such as desiccation (removal of water from a body at an extreme stage) or freezing. Tardigrades are believed to only use 0.01% of their normal energy consumption when in cryptobiosis. They have already been shown to survive spaceflight and even exposure to space vacuum in previous studies.
Thomas Boothby of the University of Wyoming says tardigrades have "remarkable" resilience compared to almost any animal, but interstellar travel is much more extreme than low Earth orbit. “I think the tardigrades could teach us a lot of things about how we humans might get along. One of the main lessons from this type of experiment would probably be to identify the tricks used by tardigrades to survive and use these to try to develop therapies or countermeasures for humans facing the stress of (interstellar) travel,” he explains. But one day we will be able to benefit from some of their superpowers thanks to the genetic editing.
"Sending small cryptobiotic life forms as model organisms may pave the way for the search for more complex and less robust organisms in interstellar space," the researchers write in their paper. “The information presented in this study aims to facilitate the design and elucidate the experimental space currently available for interstellar space biology missions. Future work in developing more sophisticated interstellar biosentinel experiments and hardware design, which will lead to a deeper understanding of our own biology and the worlds around us, will be one of humanity's greatest endeavors”, they conclude.
Reference:
Interstellar space biology via Project Starlight
by Stephen Lantin, Philip Lubine Acta Astronautica Volume 190, January 2022, Pages 261-272 DOI: 10.1016/j.actaastro.2021.10.009