Earth-Sized Exoplanets in Habitable Zones

How did the microbiological experiments on the two Viking landers work?

they searched for metabolic reactions in the samples

Which Viking experiment delivered results that were exactly as expected for the presence of living microbes in the soil sample?

The Label Release (LR) experiment

Which measurement performed by Viking, which was not part of the microbiological experiments, convinced most scientists in the late 1970s that Viking had not found life on Mars?

the absence of any detectable amount of organic compounds in the soil samples

Which new discovery has called our negative interpretation of the results of the Viking microbiological experiments - at least - into question?

The discovery of perchlorate in the Martian soil, a strong oxidizer that can react with organic compounds at the temperatures of the Viking experiments

If life ever emerged on Mars, what is the most likely place for it to exist today?

In the subsurface where it is protected against the harsh UV radiation

Which one of the following is not a requirement for the amount of tidal heating that Io and Europa experience?

the strong magnetic field of Jupiter

In order for life to be possible on Jovian moons, far outside the classic habitable zone, which one of the following is not required for this?

a very dense atmosphere

Titan is an interesting moon for astrobiology. Why?

its dense atmosphere contains organic molecules and it even has liquids on the surface

Enceladus, a small moon of Saturn, also turned out to be an interesting place for astrobiology, why?

(c) its icy geysers indicate the presence of liquid water in some parts below the surface

Why is it usually very difficult (or even impossible) to directly image exoplanets around distant stars?

Because the faint image of the planet is overwhelmed by the super-bright image of the star

Why does the radial velocity method of detecting extrasolar planets only give us the minimum mass of a planet, i.e. a lower limit?

b. because we don't know the angle the planet's orbit makes with our line of sight

Which planet is most likely to be detected by the radial velocity technique?a. A small planet orbiting close to its star

b. A massive planet orbiting close to its star

Which planet is most likely to be detected by the transit technique?

b. A large planet orbiting close to its star

Two planets were discovered using the radial velocity method and have nearly identical masses, but the Kepler mission found that planet 1 appears to be two times larger in diameter than planet 2. Which of the following is true?

d. The density of planet 2 must be greater than that of planet 1.

What is the main reason why the Kepler telescope was launched into space?

because our atmosphere is too variable to find the small transit signals of Earth-size planets

Which kind of planets were found most frequently by Kepler ?

Super-Earths (between 1.4 and 2.8 Earth radii)

What is so remarkable about the Trappist-1 planetary system?

It consists of seven Earth-size transiting planets in a compact orbital configuration

What is/are examples for possible biosignatures?

The large abundance of free oxygen in Earth's atmosphereo The seasonal variation in Mars's atmospheric methane abundanceo The characteristic change in surface reflectivity due to the presence of vegetationo The seasonal variation in Earth's atmospheric CO2 abundanceo All of the above

Q: Our best hope for determining that life on an extrasolar world lies in

Obtaining spectra that allow us to determine atmospheric composition

Why do most astronomers think that the search for biosignatures - and not SETI - will more likely lead to the first detection of probably extraterrestrial life?

Because even life on Earth was microbial for most of its time

How did the microbiological experiments on the Viking landers work?

hey searched for metabolic reactions in the samples

What were the results of the 3 Viking microbiological experiments testing the original Martian soil samples and then the heat-sterilized control samples?

all 3 samples gave positive results, but 2 out of 3 controls gave positive results as well

Subsequent missions to Mars found that perchlorate is a common compound of the Martian soil. Why does that discovery allow to view the Viking data in a new light, and potentially even re-interpret them?

because it destroys organic material when heated up by the old Viking experiment

Today, scientist no longer regard the evidence for ancient Martian microbes in the meteorite AHL 84001 as compelling enough. However, there is still one line of evidence that has not been completely refuted. Which one?

The presence of magnetic mineral structures that could have been formed by magnetotactic microbes

Which possible biosignature was detected in Mars's atmosphere both by the Curiosity rover and by Earth-based telescopes?

A seasonal variation in gaseous methane (CH4)

What is terraforming?

The process by which human technology can turn a planet into a more Earth-like world

Why did we discuss the moons of the giant planets in our course? Aren't they way too far away from the Sun?

Because we found that these moons have additional energy sources and can potentially host ecosystems totally independent from sunlight

he raising of tidal bulges by strong tidal forces from a planet on a moon is the first requirement for tidal heating. What is the second requirement?

That the orbit of the moon is not perfectly circular

Io is covered in volcanoes while Europa is covered in ice because

Io is subject to stronger tidal heating than Europa

Why is the subsurface liquid water ocean on Europa much more exciting for astrobiology than the subsurface oceans on Ganymede (or Titan)?

Because Europa's ocean can exchange material (e.g organics and oxygen) with the icy surface and the rocky seafloor, the others cannot

We discussed Saturn's large moon Titan in our class, mainly because:

Because its surface and atmosphere contain organic molecules akin to the Miller-Urey experiment

In general though, the chances for life on Titan's surface are considered slim, mainly because

The surface temperature is far below the freezing point of water

Enceladus, a small moon of Saturn, also turned out to be an interesting place for astrobiology, why?

its icy geysers indicate the presence of liquid water in some parts below the surface

Why is it so difficult to directly image an exoplanet?

ver interstellar distances the planet appears too close to a much brighter light source, the star

Why can we detect exoplanets using indirect methods, like the radial velocity technique?

because the star and planet both orbit their common center of mass

How exactly does the radial velocity method detect the presence of planets around other stars?

It uses the Doppler effect to measure the velocity of the star along the line of sight

Which parameter(s) can we obtain with the radial velocity method?

the minimum mass of the planet, its orbital period, and eccentricity

How does the transit technique detect the presence of planets around other stars?

It uses measurements of the amount of light that we receive from the target star and checks for a small dimming when the planet crosses in front of the star

Which parameter(s) can be measured directly with the transit method?

he radius of the planet, the orbital period and the transit duration

The very first extrasolar planets ever discovered by humans were found orbiting

A pulsar

What has been a major surprise from the initial results from radial velocity searches for extrasolar planets?

Many of the extrasolar planets had eccentric orbits and shorter periods than Jupiter.

Ground-based exoplanet surveys detected mostly gas giant planets and a smaller fraction of Neptunes and Super-earths. Of course, this result was affected by selection effects. What are the fractions like by today's count of exoplanets?

Gas giants like Jupiters are in the minority, Super-Earths dominate.

What was the primary science goal of NASA's Kepler mission?

determine the frequency of Earth-size planets in the habitable zone of sun-like stars

The Kepler mission has monitored approximately 160,000 stars for transits. Based on the overall detection statistics of the 4-year survey, which of the following would be a reasonable conclusion?

Most stars have small planets with orbital periods of one year and less.

A recent analysis of the Kepler data told us something important about the frequency of approximately Earth-sized planets orbiting in the habitable zone of their parent stars. What did it tell us?

That there are at least a few hundred million planets of this type in our galaxy

Bonus question 1 (Q26): there is the interesting possibility of oxygen making its way into the subsurface ocean of Europa. Where is the oxygen coming from?

It is produced by the impacts of high energy particles on the icy surface of Europa

Bonus question 2 (Q27): the geometric transit probability of a hot Jupiter is 10%. You perform a transit survey and observe a star cluster with exactly 10,000 stars and you detect 100 hot Jupiters! What can you conclude from this?

1,000 stars in this cluster are orbited by hot Jupiters