Attack on Titan

NASA announced last week that it had selected the Dragonfly mission to explore the prebiotic organic chemistry and look for signs of life on Titan. At 3,200 miles (5,150 km) across, Titan is the largest moon orbiting Saturn and the second-largest natural satellite in the Solar System. Larger than both the Moon and the planet Mercury.

Image result for Titan

Because it is so far from the Sun, about 886 million miles (1.4 billion km), its surface temperature is minus 290 degrees Fahrenheit (minus 179 degrees Celsius). Its surface pressure is also 50% higher than Earth’s.

Titan has a dense, nitrogen-based atmosphere like Earth. Unlike Earth though, it has clouds and rain made of methane. The moon’s weather and surface processes have combined complex organics, energy, and water similar to those that may have sparked life on our planet. Other organics are formed in the atmosphere and fall like light snow.

The Mars rover-size, drone-like vehicle will have eight rotors and will fly to dozens of promising locations on Titan looking for prebiotic chemical processes common on both Titan and Earth.

Dragonfly will visit a world filled with a wide variety of organic compounds, which are the building blocks of life and could teach scientists about the origin of life itself. The rotorcraft will fly for miles across the organic sand dunes of Saturn’s largest moon, investigating the processes that shape Titan’s extraordinary environment.

It will take advantage of Titan’s dense atmosphere to become the first vehicle ever to fly its entire science payload to new places for repeatable and targeted access to surface materials.

During its 2.7-year baseline mission, Dragonfly will explore diverse environments from the organic dunes to the floor of an impact crater where liquid water and complex organic materials key to life once existed together for possibly tens of thousands of years.

Dragonfly is scheduled to launch in 2026 and reach Titan in 2034.

Could Moons Contain Life?

According to new research, exomoons (natural satellites of planets outside our Solar System) could offer another clue about the pool of alien worlds that may be home to life.

Only a small proportion of exoplanets are likely to be able to sustain life, existing in the habitable zone of their stars. But some planets, especially large gas giants, may harbor moons which contain liquid water.

These moons can be internally heated by the gravitational pull of the planet they orbit, which can lead to them having liquid water well outside the normal habitable zones of systems that scientists are trying to find Earth-like planets in.

Researchers looked at the possibility of exomoons orbiting J1407b, a large gas giant believed to have an enormous ring system. J1407b circles a 16-million-year-old Sun-like star approximately 434 light-years away from Earth. The planet’s mass is thought to be in the range of about 10 to 40 Jupiter masses.

The rings of J1407b are shown eclipsing the young Sun-like star J1407. Image credit: Ron Miller.

J1407b

Scientists ran computer simulations to model the rings around J1407b, which are 200 times larger than those around Saturn. Gravitational forces between particles were calculated and used to update the positions, velocities, and accelerations in the computer models of J1407b and its ring system. They then added a moon that orbited at various ratios outside of the rings to test whether this caused gaps to form where they expected.

The findings revealed that while the orbiting moon did have an effect on the scattering of particles along the ring edge, the expected gaps in the ring structure were unlikely to be caused by the gravitational forces of a currently unseen moon orbiting outside J1407b’s rings.

The paper was published in the Monthly Notices of the Royal Astronomical Society.

A Better Way to Look

K-type dwarf stars are dimmer than the Sun but brighter than faint stars. These stars live for a very long time, 17 to 70 billion years, compared to 10 billion years for the Sun. This gives plenty of time for life to evolve on any planets in their habitable zones. Also, they have less extreme activity in their youth than M-type stars (red dwarfs), the most common star type in the Milky Way Galaxy.

K-stars may be in a ‘sweet spot’ between Sun-analog stars and M-type stars astronomers at NASA’s Goddard Space Flight Center and writers of a paper published in the Astrophysical Journal Letters.

Scientists consider the simultaneous presence of oxygen and methane in a planet’s atmosphere to be a strong biosignature because these gases like to react with each other, destroying each other. So if they are present in an atmosphere together, that implies something is producing both of them quickly, quite possibly life.

However, because exoplanets are so remote, there needs to be significant amounts of oxygen and methane in an exoplanet’s atmosphere for it to be seen by observatories on Earth. The researchers found that the oxygen-methane biosignature is likely to be stronger around a K-type star than a Sun-like star.

This stronger oxygen-methane signal has also been predicted for planets around M-type stars, but their high activity levels might make M-stars unable to host habitable worlds. K-type stars can offer the advantage of a higher probability of simultaneous oxygen-methane detection compared to Sun-like stars without the disadvantages that come along with an M-star host.

Additionally, exoplanets around K-type stars will be easier to see than those around Sun-like stars simply because K-stars are dimmer. The Sun is 10 billion times brighter than an Earth-like planet around it. That’s a lot of light you have to suppress if you want to detect an orbiting planet. A K-star might be ‘only’ a billion times brighter than an Earth-like planet orbiting it.