My first Magazine Sky & Telescope - 02.2019 | Page 26

Why do we care how complex the atmospheric chemistry We need to know what kinds of is? One of the big questions we are interested in answering molecules are made only by life is how far organic chemistry can proceed in the absence of life. We know from analyzing meteorites that compounds like so that we can use them to detect amino acids (the building blocks of proteins) can be produced life both in the solar system and by abiotic processes. With Titan, we can begin to understand how far abiotic organic chemis- elsewhere. try can proceed in an atmosphere. This is important for two reasons. First, #2 Carbon we need to know what kinds of molecules are was complex, we knew we needed to study Titan’s atmosphere monoxide made only by life so that we can use them to further to investigate these questions. detect life both within the solar system and elsewhere in To explore what the Cassini orbiter and Huygens probe have the universe. Many of the molecules used by life on Earth, taught us about chemistry on Titan, let’s take a trip into the like amino acids and nucleobases (the building blocks of atmosphere, starting at the top and working our way down. DNA and RNA), are not unique to biotic processes: They’re also produced without life’s involvement and are found in Ionosphere: Surprise Super-Molecules meteorites and comets. But their relative amounts in these The Ion and Neutral Mass Spectrometer (INMS) was the pri- environments are different than what we find mary instrument designed to measure the composi- when they’re created by life on Earth. So we need tion of Titan’s ionosphere as Cassini repeatedly flew to study abiotically produced organic molecules through it during the spacecraft’s mission. INMS in order to be able to tell the difference between measured the composition of the atmosphere by abiotic sources and biotic ones when looking at measuring the masses of the molecules it ingested. other planets. The team had designed the instrument to cover a #3 Second, we want to understand the role that mass range of 1 to 99 atomic mass units, which Ethane planetary atmospheres play in the origin and evo- roughly covers atomic hydrogen (1) to molecules lution of life. One potential role is to provide material (like with approximately six to seven “heavy atoms” like carbon, organic molecules) to help life get started and/or to evolve. nitrogen, or oxygen. This mass range easily included the Since we realized, even before the arrival of Cassini-Huygens, heaviest molecule known to exist in Titan’s atmosphere when that the organic chemistry occurring in Titan’s atmosphere it was designed (C 2 N 2 , with an atomic mass of 52) and the q TITAN’S SURFACE These infrared images combine 13 years of Cassini’s visible and near-infrared imagery into smooth mosaics of the surface that hides beneath Titan’s thick atmosphere. Reddish brown marks the moon’s equatorial dune fields, while the bluish and purplish regions might be enriched in water ice. The central longitudes of each view are (from left to right) approximately 30°, 60°, 120°, 210°, 300°, and 330° west. 24 FE B RUA RY 2 019 • SK Y & TELESCOPE Alien “Earth” Next Door