 Microgravity: living on the International Space Station

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

# 6 The habitability of planets

There is continuous research into finding exoplanets outside the Solar System with environments similar to Earth’s. But how is this done?

A range of techniques are used. For example, the measurements of planets can be plotted on a graph similar to Figure 6. Here, the orbital radius is measured in terms of astronomical units (AU). This is the distance from the Earth to the Sun (150 million km). The planet’s mass is measured relative to the mass of the Earth (ME) (6 × 1024 kg).

Using Figure 6, now complete Activity 8. Figure 6 A graph used to plot other planets.

## Activity 8 Exploring the habitability of other planets

Allow approximately 15 minutes

Choose the correct answer to the following questions.

1. Which values are plotted on the horizontal axis?

a.

Orbit

b.

Orbit radius

c.

Planet mass

d.

Orbit radius/AU

e.

Planet mass/ME

The correct answer is d.

2. Which values are plotted on the vertical axis?

a.

Orbit

b.

Orbit radius

c.

Planet mass

d.

Orbit radius/AU

e.

Planet mass/ME

The correct answer is e.

3. Where would you expect to find Earth? (Hint: Earth is at a distance of 1 AU from the Sun and has a relative mass of 1 ME.

a.

J

b.

S

c.

E

d.

V

e.

N

The correct answer is c.

4. The planets labelled V, E, J, S and N are in our Solar System. Which one has the largest relative mass?

a.

J

b.

S

c.

E

d.

V

e.

N

The correct answer is a.

5. Which planet has the smallest orbital radius?

a.

J

b.

Me

c.

E

d.

V

e.

Ma

The correct answer is b.

What makes planets habitable for humans?

You might have heard of the ‘Goldilocks zone’. This is the zone occupied by the Earth in its orbit about the Sun. This zone is neither too close to the Sun – that is, too hot – nor too far away from the Sun – that is, too cold. So, Earth is located where the conditions are just right for life to exist.

In trying to find other planets which are suitable for humans, the Planetary Habitability Laboratory (PHL) aims to map the habitable Universe. It holds the Habitable Exoplanets Catalogue (HEC) which lists and compares potentially habitable exoplanets (Figure 7). Using this information in Figure 7, now complete Activity 9. Figure 7 Potentially habitable exoplanets ranked by distance from Earth in light years (ly). Kapteyn b, GJ 667 C e and GJ 667 C f are planet candidates.

## Activity 9 Potentially habitable exoplanets

Allow approximately 15 minutes

Answer the following questions, choosing one option for each.

1. Which planet is closest to Earth?

a.

Trappist-1 f

b.

Kepler-62 f

c.

GJ 667 C c

d.

Proxima Cen b

e.

Kepler-1229 b

The correct answer is d.

2. According to Figure 7 only, what is the greatest distance of an exoplanet from Earth?

a.

1200 ly

b.

770 ly

c.

1115 ly

d.

2000 ly

e.

39 ly

The correct answer is a.

3. Which one of the following is a ‘planet candidate’?

a.

Trappist-1 f

b.

Kepler-62 f

c.

GJ 667 C c

d.

Proxima Cen b

e.

Kepler-1229 b

The correct answer is c.

Next you will complete the end-of-week quiz.

MG_1

### Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus