by Thomas Kitchen
Staff Writer
The prospect of venturing beyond our planet has captivated the minds of humans for millennia. Over the last decades, humans have sent thousands of spacecraft into orbit around Earth and into the Solar System, but only a measly 5 have ever traveled the roughly 11 billion miles (120 astronomical units) to the heliopause. The heliopause is the region of space where the solar wind meets the interstellar medium, or to put it simply, the beginning of interstellar space. The reason why very few spacecraft have made the journey is because it takes decades for a traditional chemical propulsion to travel that distance. Due to this long travel time, it isn’t feasible to send humans beyond Mars anytime soon. So, a group of researchers in this study discuss the practicality of sending microorganisms to interstellar space through Project Starlight to test the effects interstellar space has on life. Project Starlight is a NASA program that aims to use large scale directed energy to propel small spacecraft to relativistic speeds to enable interstellar missions.
Previous Interstellar missions have sent messages in the event they are found by extraterrestrials. In 1972 and 1973, Pioneer 10 and 11 were launched into space with plaques depicting the human form, and the location of the solar system in relation to pulsars. What can be sent into interstellar space via a swarm of laser-sail spacecraft is wider in scope, but how can humans get a spacecraft out into interstellar space in a reasonable period of time? A laser-sail spacecraft works when photons from light bump into a spacecraft, their momentum is transferred and the spacecraft is propelled a bit. This is also how a solar sail works. By using a large array of modular lasers humans can propel a wafer-size spacecraft to relativistic speeds. An array of lasers like this could also be used to deflect hazardous space objects and vaporize space junk.
How would Earth communicate with a spacecraft the size of a wafer in interstellar space?
Due to the size of a singular spacecraft what can be put on it in terms of hardware would be severely limited because they need to carry regular experiments as well as biosentinel experiments. It takes roughly 21 and a half hours to speak with the voyager one probe which is the farthest spacecraft from earth at about 14.4 billion miles away from Earth. The small wafer-sized spacecraft would be in a swarm so multiple spacecraft could serve as a relay for all of the spacecraft carrying experiments. Aggressive compression of data will make communication as energy efficient as possible and allow for a good link with the swarm and Earth.
Now that the spacecraft is ready, the study focuses on sending life to interstellar space. So what gets to make the journey and what criteria do they have to meet? Hypergravity is defined as any force exceeding one g of force. An example of this on Earth would be a fighter pilot making a sharp turn in a jet and pulling about six g’s of force. During the launch of the laser-sail spacecraft, the craft and the life inside would be subjected to the range of 104 to 106 g. As a human, this force would turn you into a fine paste. Tardigrade species are adversely affected by hypergravity but are more resistant than larger organisms like fruit flies. C. elegans (non-parasitic, really small worms) can do very well under hypergravity conditions. However, tardigrades can be launched in a cryptobiotic state which hopefully will reduce the negative effects of hyper acceleration and increase survivability. The organisms would need to be put in a cryptobiotic state, which is just a much deeper form of hibernation, maintaining periods of undetectable metabolic rate. The organisms can then be brought out of the cryptobiotic state when the destination is reached. The organisms would also need a high radiation tolerance. The radiation the organisms would be subjected to in Low Earth Orbit would be minimal since Earth's magnetic field provides protection from radiation. Unfortunately for the organisms, radiation exposure gets pretty bad outside Earth’s magnetic field and the heliopause. The organisms would be subjected to ultraviolet radiation, higher energetic solar particles (SPE) composed of gamma rays, and x-rays. The shielding on the spacecraft would provide some protection, but radiation produced during SPE can pass through most lightweight material. Human side effects on the same journey could include radiation sickness and cancer.
So given our criteria, who gets to go?
Tardigrades are microscopic organisms known for their robustness. They are found in multiple habitats of fresh waters and oceans all across the seven continents. Tardigrades are not true extremophiles because they can endure but not necessarily thrive in harsh conditions. Given water bears ability to be put in a cryptobiotic state, it makes them a prime candidate for interstellar astronauts where resources will be very few. Hydrated and dehydrated Tardigrades have already been to space in previous projects in Low Earth Orbit and have shown high survival rates in open space while shielded from UV radiation. In humans, microgravity and space radiation can cause oxidative stress that upsets the homeostasis. Though oxidative stress can occur in Tardigrades, they have natural defense mechanisms to mitigate the effects of oxidative stress. The scientist in the study also suggests that genetically modifying Tardigrades to be more desirable for the journey to interstellar space should also be an option to consider.
The study noted a few more organisms but highlighted Tardigrades as the best candidate. As humanity is steadily growing to the ability of interstellar travel, the importance of sending life outside the solar system increases, as it offers an opportunity to “study biological systems under microgravity and space radiation conditions unique to interstellar space.” As stated in section seven of the study. It will also bring us closer to the answer of the question, “can humans travel to other solar systems?”