Radiation makes ice act like a liquid, a helpful state for growing organic molecules
K. Getman et al/PSU/CXC/NASA (X-ray); J. Wang et al CfA/JPL-Caltech/NASA (IRL)
Ice in space may break out the bubbly. Zapping simulated space ice with imitation starlight makes the ice bubble like champagne. If this happens in space, this liquidlike behavior could help organic molecules form at the edges of infant planetary systems. The experiment provides a peek into the possible origins of life.
Shogo Tachibana of Hokkaido University in Sapporo, Japan, and colleagues combined water, methanol and ammonia, all found in comets and interstellar clouds where stars form, at a temperature between ‒263° Celsius and ‒258° C. The team then exposed this newly formed ice to ultraviolet radiation to mimic the light of a young star.
As the ice warmed to ‒213° C, it cracked like a brittle solid. But at just five degrees warmer, bubbles started appearing in the ice, and continued to bubble and pop until the ice reached ‒123° C. At that point, the ice returned to a solid state and formed crystals.
“We were so surprised when we first saw bubbling of ice at really low temperatures,” Tachibana says. The team reports its finding September 29 in Science Advances.
Follow-up experiments showed fewer bubbles formed in ice with less methanol and ammonia. Ice that wasn’t irradiated showed no bubbles at all.
Analyses traced spikes of hydrogen gas during irradiation. That suggests that the bubbles are made of hydrogen that the ultraviolet light split off methane and ammonia molecules, Tachibana says. “It is like bubbling in champagne,” he says — with an exception. Champagne bubbles are dissolved carbon dioxide, while ice bubbles are dissolved hydrogen.
Story continues after video
TOIL AND TROUBLE This video inside a super-chilled (about ‒145° Celsius) chamber shows bubbles forming and popping in irradiated ice. The experimental apparatus is known as PICACHU, or Photochemistry in Interstellar Cloud for Astro-Chronicle in Hokkaido University. S. Tachibana et al/Sci. Adv. 2017
The irradiated ice took on another liquidlike feature: Between about ‒185° C and ‒161° C, it flowed like refrigerated honey, despite being well below its melting temperature, Tachibana adds.
That liquidity could help kick-start life-building chemistry. In 2016, Cornelia Meinert of the University Nice Sophia Antipolis in France and colleagues showed that irradiated ice forms a cornucopia of molecules essential to life, including ribose, the backbone of RNA, which may have been a precursor to DNA (SN: 4/30/16, p. 18). But it was not clear how smaller molecules could have found each other and built ribose in rigid ice.
At the time, critics said complex molecules could have been contamination, says Meinert, who was not involved in the new work. “Now this is helping us argue that at this very low temperature, the small precursor molecules can actually react with each other,” she says. “This is supporting the idea that all these organic molecules can form in the ice, and might also be present in comets.”
S. Tachibana et al. Liquid-like behavior of UV-irradiated interstellar ice analog at low temperatures. Science Advances. Published online September 29, 2017. doi: 10.1126/sciadv.aao2538.
C. Crockett. Key sugar for life could have formed in space. Science News. Vol. 189, April 30, 2016, p. 18.
C. Crockett. Cyanides around young star signal complex organic chemistry. Science News. Vol. 187, May 2, 2015, p. 10.
B. Mole. Interstellar chemical resembles building blocks of life. Science News. Vol. 186, November 1, 2014, p. 7.
R. Cowen. More space sugar. Science News. Vol. 166, October 9, 2004, p. 237.