Across the Universe
In Sept., NASA confirmed evidence that liquid water flows on the surface of Mars. This is a huge discovery; prior to that the only place in the universe with flowing liquid water was the Earth.
Astronomers used the Mars Reconnaissance Orbiter (MRO) to discover the probable flows. One of the instruments on MRO called HIRISE images the Martian surface with incredible resolution, roughly 1 foot from an altitude of 186 miles. For comparison, the satellite maps on Google Maps are about 3 feet resolution from a similar altitude. Within the HIRISE images, the astronomer who made the discovery, Lujendra Ojha, observed dark narrow streaks appearing and disappearing on the planet’s surface as the seasons changed. In the warmer months, the dark streaks darkened and looked like they flowed down slopes. In the colder months, the streaks disappeared.
Images only provide so much information into an astronomical phenomenon. On Earth, geologists can physically go and sample a rock or substance that appears but we cannot do that yet for Mars. The areas where the streaks appear are not areas accessible by either rover.
Astronomers need a tool that allows them to determine the composition without taking a physical sample. Fortunately, MRO contains just the tool needed for the job: a spectrograph named CRISM that is designed to produce detailed maps of the surface mineralogy of Mars.
The team compared the HIRISE images with the CRISM maps. When the dark features appeared on the HIRISE images, the CRISM maps showed hydrated salts or salts dissolved in water in the corresponding areas. When no dark features appeared on HIRISE hydrated salts were seen on the maps. The hydrated salts belong to a category called perchlorates. The presence of perchlorates in water drops the freezing point, sometimes to as low as –94 degrees Fahrenheit. Perchlorates occur naturally on the Earth, often in the desert. Think of them as acting like antifreeze in a car or salt on the road in the winter. And no, we probably cannot drink the briny water in its current form.
The evidence implies that water mixed with hydrated salts are found on Mars, probably just below the surface. When the temperature increases, the hydrated salts melt and flow underground, moistening the soil above and causing the dark streaks detected by Ojha.
Because Mars is one of the Earth’s closest neighbors, the planet is too bright for many of the Maunakea Observatories to observe. The Submillimeter Array (SMA) is an exception. SMA’s very first image was a picture of Mars. While the discovery of liquid flowing water on Mars is new, astronomers realized years ago that water exists on Mars. SMA mapped the isotopic variants of water on the planet. Water is comprised of three atoms: two hydrogen and one oxygen, H2O. But the mass of those three atoms can vary. The variations, called isotopes, cause the different types of water to have slightly different properties. Water isotopes form under different circumstances, so they provide clues into the water’s origin and aid in tracing the history of Martian water and atmosphere.