A team of European scientists have shown that DNA molecules can withstand the rough temperatures and pressures that rockets experience when they reenter Earth’s atmosphere from space. Their finding is important from the perspective of meteorites and other space rocks that crash on Earth. Many scientists think such objects could once have seeded our planet with the first molecules of life, billions of years ago.
The scientists had attached bits of plasmid DNA – the part physically separated from chromosomal DNA in biological cells and capable of reproducing independently – on 15 different parts of the outer shell of a TEXUS mission sounding rocket (powered by the Brazilian VSB-30 motor). On March 29, 2011, the rocket took off from the European Space and Sounding Rocket Range near Kiruna, Sweden, for a suborbital flight that exposed the DNA to the vacuum and low temperatures of space before shooting back toward Earth, exposing the samples to friction against the atmosphere.
The entire flight lasted 780 seconds and reached a height of 268 km. While going up, the acceleration maxed at 13.5 g and while coming down, 17.6 g. When outside Earth’s atmosphere, the rocket and samples also experienced about 378 seconds of microgravity. The maximum temperature experienced during atmospheric reentry was just below 130 degrees Celsius on the surface of the rocket; the gases in the air around the samples attached to the sides of the rocket could have reached 1,000 degrees Celsius.
In all, a maximum of 53% of the DNA could be recovered intact and 35% was fully biologically functional. Analysis also showed that “DNA applied to the bottom side of the payload had the highest degree of integrity followed by the samples applied in the grooves of the screw heads”, according to the study paper. It was published in PLOS ONE on November 26.
The ability of the DNA molecules to sustain life was then recorded by observing how many bacterial colonies each of the 15 samples could engender per nanogram. The 100% transformation efficiency was set at 1,955 colonies/nanogram, which was what an unaffected bit of plasmid DNA could achieve.
Curiously, for sample #1, which was attached on the side of the rocket where there was minimum shielding especially during atmospheric reentry, 69 colonies/nanogram were identified. The highest density of colonies was for sample #10, which was attached in the grooves of screw-heads on the rocket: 1,368/nanogram.
“We were totally surprised,” said Cora Thiel and Oliver Ullrich, coauthors of the study and biologists at the University of Zurich, in a statement. “Originally, we designed this experiment as a technology test for biomarker stability during spaceflight and reentry. We never expected to recover so many intact and functional active DNA.”
Last molecule standing
It’s clear that the damage inflicted on the DNA samples by the harsh conditions of acceleration, microgravity, temperature fluctuations, solar radiation and cosmic rays may not have been sufficient in deterring the molecules from retaining their biological functions. In fact, this study imposes new lower limits on the survivability of life: it may not be as fragile as we like to think it is.
Scientists have known temperature to be the most effective destroyer of DNA double-strands. Studies in the past have shown that the molecules weren’t able to withstand more than 95 degrees Celsius for more than five minutes without becoming denatured. During the TEXUS-49 mission, bacterial plasmid DNA temporarily withstood up to 130 degrees Celsius, maybe more.
By extension, it is not inconceivable that a fragment of a comet could have afforded any organic molecules on-board the same kind of physical shielding that a TEXUS-49 sounding rocket did. Studies dating from the mid-1970s have also shown that adding magnesium chloride or potassium chloride to the DNA further enhances its ability to withstand high temperatures without breaking down.
How big a hurdle is that out of the way? Pretty big. If DNA can put itself through as much torture and live to tell the tale, there’s no need for it to have been confined to Earth, trapped under the blanket of its atmosphere. In fact, in 2013, scientists from the Indian Center for Space Physics were able to show, through computer simulations, that biomolecules like DNA bases and amino acids are capable of being cooked up in the interstellar medium – the space between stars – where they could latch on to trespassing comets or asteroids and bring themselves into the Solar System.
According to the study, published in New Astronomy in April 2013, cosmic rays from stars can heat up particles in the interstellar medium and promote the formation of so-called precursor molecules – such as methyl isocyanate, cyanamide and cyanocarbene – which then go on to form amino acids. The only conditions his team presupposed were a particle density of 10,000-100,000 per cubic centimeter and an ambient temperature of 10 kelvin to say about 1 gram of amino acids could be present in 1014 kg of matter.
Compared to the mass density of the observable universe (9.9 × 10-27 kg/m3), that predicted density of amino acids, if true, is quite high. So, the question arises: Could we be aliens?
The first experiments
The first studies to entertain this possibility and send hapless living things to space and back began as far back as 1966, in the early days of the Space Age, alongside the Gemini IX and XII missions. Prominent missions since then include the Spacelab 1 launch (1983), the Foton 9, 11 and 12 rockets (1994-1999), the Foton M2 and M3 missions (2005-2007) and ISS EXPOSE-R mission (2009-2011). The Foton launches hosted the STONE and BIOPAN missions, which investigated if microbial lifeforms such as bacteria and fungi could survive conditions in space, such as a low temperature, solar radiation and microgravity.
Through most of these missions, scientists were able to find that the damage to lifeforms often extended down to the DNA-level. Now, we’re one step closer to understanding exactly what kind of damage is inflicted, and if there are simple ways for them to be fended off like with the addition of salts.
The STONE-5 mission (2005) was particularly interesting because it also tested how rocks would behave during atmospheric reentry, being a proxy for meteorites. It was found that the surface of a rock reached temperatures of more than 1,800 degrees Celsius. However, mission scientists concluded that if the rock layer had been thick enough (at least more than 5 mm as during the test, or 2 cm during STONE-6) to provide insulation, the innards could survive.
In the same vein, the ultimate experiments – though not performed by humans – could have been the Murchison meteorite that crashed near a town of the same name in Australia in 1969 and the Black Beauty, a rock of Martian origins, that splintered over the Sahara a thousand years ago. The Murchison meteorite was found to contain more than 70 different amino acids, only 19 of which are found on Earth. The Black Beauty was found to be 4.4 billion years old and made of sediments, signalling that a young Mars did have water.
Their arrivals’ prime contribution to humankind was that they turned our eyes skyward in the search of our origins. The experiments conducted with the TEXUS-49 mission keep them there.