AST101: The Sun and its Neighbours

Class 20: Exploring the Solar System

Professor C. Barth Netterfield
 Atmospheric Absorption

The atmosphere
100 %
Most light reaches surface absorbs and
scatters light.
relative transmission

Not all
wavelengths of
50 % light can travel
through the
atmosphere.
No light reaches surface
The atmosphere
is opaque at some
100 nm 1 µm 10 µm 100 µm 1 mm 10 mm 100 mm wavelengths.
wavelength
VIS

X-ray UV IR far IR submm microwave radio

[Cepheiden, modified]

Class 20: Exploring the Solar System | Prof. Netterfield

Telescopes in Space!
The Herschel Space Observatory
observed sub-mm Light.

[NASA]

The Chandra Space Telescope observes

X-Ray light.

[ESA - D. Ducros]

Class 20: Exploring the Solar System | Prof. Netterfield

 Atmospheric Absorption

The atmosphere
100 %
Most light reaches surface absorbs and
scatters light.
relative transmission

Not all
wavelengths of
50 % light can travel
through the
atmosphere.
No light reaches surface
The atmosphere
is opaque at some
100 nm 1 µm 10 µm 100 µm 1 mm 10 mm 100 mm wavelengths.
wavelength
VIS

X-ray UV IR far IR submm microwave radio

[Cepheiden, modified]

Class 20: Exploring the Solar System | Prof. Netterfield

Class 20: Exploring the Solar System | Prof. Netterfield
 Astronomical Seeing

Turbulence in the Earth’s

atmosphere distorts images.

For long exposures and

large telescopes (required
for dim objects) this blurs
the image.

Without corrective
measures, resolution for
ground based telescopes is
limited.

[Philipp Salzgeber]

Class 20: Exploring the Solar System | Prof. Netterfield

Telescopes in Space!

The Hubble Space

Telescope operates in
Earth Orbit, above the
atmosphere.
[NASA/STSCI/A.Riess]

The Hubble Space Telescope has resolution 5 to 10 times better

than the best seeing-limited ground based telescopes.

Class 20: Exploring the Solar System | Prof. Netterfield

Pictures from the Hubble space Telescope
in Earth Orbit.

Pluto

Jupiter
Mars
Images of some of the
planets by the Hubble Europa Can’t measure: Gravity, magnetic
Space Telescope. [NASA] fields, radiation ...
Class 20: Exploring the Solar System | Prof. Netterfield
Instant Quiz: (60 s)
PollEv.com/uoftastro
Telescopes are put in space...

A)To get closer to the objects

they are looking at.
B)To avoid the effect of the
atmosphere
C)So they can be more stable in
orbit (free fall)
D)All of the above
E)None of the above

Class 20: Exploring the Solar System | Prof. Netterfield

Space is big
Minimum Distance Jet Travel Time Travel Time at
(km) (903 km/hr) 20,000 km/hr

Moon 384,000 km 2.5 weeks 19.2 hours

Mars 227,939,200 km 9.9 years 5.4 months

Jupiter 778,570,000 km 79.5 years 3.6 years

Neptune 4,500,000,000 km 550 years 24.8 years

Class 20: Exploring the Solar System | Prof. Netterfield

 The New Horizons probe to Pluto

Pluto Initial
speed was
58,500
km/hr.

9.5 year
travel time
to Pluto.
(Jan 6,
2006 – July
14, 2015)

Passed Pluto
travelling
52,200
km/hr.
Arrokoth
[Pheonix777 CC BY_SA 4.0]

Class 20: Exploring the Solar System | Prof. Netterfield

Class 19: Exploring the Solar System | Prof. Netterfield
 Voyager Probes

● In 1977, the alignment of

planets was just right to
visit all 4 Jovian Planets
with one probe.
● It used each planet’s
gravity to accelerate and
change direction to the
next planet (“Slingshot”)
● Two were launched –
Voyager 1 and Voyager 2.
● They are still operating,
20 light-hours from
Earth!

[Phoenix7777 CC BY SA 4.0]
Class 20: Exploring the Solar System | Prof. Netterfield
 Voyager 2
Launch: August 20, 1977
Jupiter: July 9, 1979
Saturn: August 26, 1981
Uranus: January 24, 1986
Neptune: August 25, 1989

Voyager 2 is
still operating.

It is the furthest
human-made
object ever built.
[Don Davis]
[Phoenix7777 CC BY SA 4.0] Class 20: Exploring the Solar System | Prof. Netterfield
 Gravity Assist (Slingshot Manoeuvre)

When a probe
flies by a
planet, gravity 40

Heliocentric velocity (km/s)

changes the Earth 20 Aug 77
probe’s speed 35
Neptune
and direction. 30 25 Aug 89
Uranus
25 24 Jan 86
Passing behind
20
speeds it up.
15 Saturn Voyager 2 velocity
25 Aug 81
Passing ahead 10
Jupiter
slows it down. 9 Jul 79
5
Solar system escape velocity
0
[David Shortt CC BY-SA 4.0] 0 5 10 15 20 25 30 35 40
Distance from sun (astronomical
[Cmglee CC BY-SA 3.0]

Class 20: Exploring the Solar System | Prof. Netterfield

 Transfer Orbit

How can you get

from one orbit to
another?

Class 20: Exploring the Solar System | Prof. Netterfield

 Transfer Orbit
(1) Start in the inner orbit

Class 20: Exploring the Solar System | Prof. Netterfield

 Transfer Orbit
(1) Start in the inner orbit
(2) Engine burn to speed up

2
Δv

Class 20: Exploring the Solar System | Prof. Netterfield

 Transfer Orbit
(1) Start in the inner orbit
(2) Engine burn to speed up
(3) Now in the transfer orbit
1

2
Δv

Class 20: Exploring the Solar System | Prof. Netterfield

 Transfer Orbit
(1) Start in the inner orbit
(2) Engine burn to speed up
3 (3) Now in the transfer orbit
1

2
Δv

Class 20: Exploring the Solar System | Prof. Netterfield

 Δv'
4 Transfer Orbit
5
(1) Start in the inner orbit
(2) Engine burn to speed up
3 (3) Now in the transfer orbit
1
(4) Do a 2nd burn to speed up

2
Δv

Class 20: Exploring the Solar System | Prof. Netterfield

 Δv'
4 Transfer Orbit
5
(1) Start in the inner orbit
(2) Engine burn to speed up
3 (3) Now in the transfer orbit
1
(4) Do a 2nd burn to speed up
(5) End in the outer orbit

No fuel is used except at the

2 burns (2) & (4).
Δv
The rest of the time, you are
coasting in an orbit.

Class 20: Exploring the Solar System | Prof. Netterfield

Mars Global Surveyor
In orbit around Mars.
Made high resolution images of Mars
from 1999 until 2006.

Class 20: Exploring the Solar System | Prof. Netterfield

Mars Global Surveyor

[NASA - MGS] Class 20: Exploring the Solar System | Prof. Netterfield
Juno Mission to Jupiter
Launched: August 5, 2011
Used both a gravity assist (from
Earth) and a transfer orbit to get to
Jupiter.
Arrived: July 5, 2016

Has 9 different instruments,

including a camera. It measures
gravity, magnetic fields, radiation,
infrared and UV spectra, and radio
emissions.

End of Mission: July, 2021

Class 20: Exploring the Solar System | Prof. Netterfield

Instant Quiz: (60 s) PollEv.com/uoftastro
The Europa Clipper was launched in
October, 2024 on its way to Europa, a
moon of Jupiter. Considering how long
the trip is, when will it arrive at
Jupiter system?

A) December, 2024
B) February, 2025
C) April, 2030
D) December 2053 Class 20: Exploring the Solar System | Prof. Netterfield
Venera 13: Mission to Venus
Launched Oct 30, 1981
Landed March 1, 1982
Parachute landing
Temperature: 457 C

Pressure: 89 atmospheres

Survived 127 minutes (!)

First Colour image from Venus.

First sound recording from another

planet.

Rock drill – analyzed rock types.

[Venera team/Don P. Mitchell]
Class 20: Exploring the Solar System | Prof. Netterfield
Mars Rovers Lots of experiments:
Cameras, drills,
NASA has sent four rovers to Mars. chemistry & geology,
Sojourner (1997), Spirit and weather, radiation, ice
Opportunity (2004) and Curiosity detection...
(2012).
Opportunity lasted 15 years and
travelled 45 km.
Curiosity is still running and
has travelled 32.4 km (as of
September 19, 2024).

Supplemental: Search YouTube for

“7 Minutes of Terror: Curiosity Rover's Risky Mars Landing”
Class 20: Exploring the Solar System | Prof. Netterfield
 OSIRIS-Rex
Sample return mission to the
Asteroid Bennu.
Will return a sample for lab
study.

Samples were placed in a return capsule on October 28, 2020. They

will return to Earth for analysis in 2023!
[NASA] Class 20: Exploring the Solar System | Prof. Netterfield
Apollo Program: People on the Moon!
6 moon landings
between 1969 and
1972.

Explored and returned

samples

Class 20: Exploring the Solar System | Prof. Netterfield

Power

Inner Solar System: Solar panels!

Convert sunlight into electricity.

Outer Solar System:

Radioisotope thermoelectric generator!
Uses radioactive plutonium to generate
electricity.

Class 20: Exploring the Solar System | Prof. Netterfield

Communications!

Spacecraft communicate with Earth using radio.

Large dishes are used to focus the very weak signals.

Data rates tend to be

very low: it took more
than a year for New
Horizons to send back
its images.

Light travel time makes for long

delays. It is a few minutes to Mars.
Round trip delay is 13h:45 to New
Horizons and 42h:06 to Voyager 1!

Deep Space Network Dish in

Goldstone, CA

Class 20: Exploring the Solar System | Prof. Netterfield

Instant Quiz: (60 s) PollEv.com/uoftastro

What is/are important challenges with communicating with

satellites in the outer solar system, such as New Horizons?
A) The long distances place long delays in communications
B) The long distances require very large antennas on Earth
in order to pick up the weak signals.
C) The weak signal from the huge distances result in very
low data rates, which means it takes a long time to
download images.
D) The large distances means that the satellites need large
antennas to produce enough signal to be detected on Earth.
E) All of the above.

Class 20: Exploring the Solar System | Prof. Netterfield

 [SpaceX] Payload
Launch Vehicles
[Bproks13 CC BY-SA 4.0]

Fuel

Oxydizer

Pumps

Engine

Falcon Heavy:
63,600 kg to Low Earth Orbit
16,800 kg to Mars
[NASA]
3,500 kg to Pluto

Class 20: Exploring the Solar System | Prof. Netterfield

Class 20: Exploring the Solar System | Prof. Netterfield