Download Phys 214. Planets and Life

Phys 214. Planets and Life
Dr. Cristina Buzea
Department of Physics
Room 259
E-mail: [email protected]
(Please use PHYS214 in e-mail subject)
Lecture 24. Searching for life in our Solar system.
Mercury, Venus, Jupiter, Saturn,
Uranus, & Neptune
March 14th, 2008
Contents
•
Textbook pages 243-255
• Biological tour of our Solar system –
Mercury, Venus, Jupiter, Saturn, Uranus, & Neptune
Mercury
Mercury
Earth
Mass (MEarth)
0.055
1
Escape velocity (km/s)
4.43
11.2
Orbital semimajor
axis (AU)
0.39
1
o
Orbital inclination ( )
7
0
Orbital period (days)
88
365
Axial rotation (days)
58.6
0.997
o
Axial inclination ( )
0.1
23.5
Radius (km)
2440
6371
3
-3
Density (x10 kg m )
5.43
5.51
-2
Surface gravity (m s )
3.7
9.8
Mean surface T (K) 443K (170C)
288K (15C)
Max surface T(K) 700K (427C)
310K (37C)
Min surface T(K) 100K (-173C)
260K (-13C)
Atmospheric surface
pressure (bar)
10-15
1
Atmosphere
O, Na, H2
N2, O2
Satellites
none
1
Largest known
surface feature
Caloris Basin Mt. Everest
(1350 km diam)
(8 km above
sea-level)
Larger than most moons, but smaller than Jupiter’s
moon Ganymede and Saturn’s moon Titan.
Mercury
•
The orbit of Mercury is the most eccentric of the planets; its eccentricity is 0.21 with its
distance from the Sun ranging from 46,000,000 to 70,000,000 kilometers.
The varying distance to the Sun, combined with a 3:2 spin-orbit resonance of the planet’s
rotation around its axis, result in complex variations of the surface temperature. Each
day and night last about three Earth months each. The dayside temperature is 427 oC,
but with no atmosphere to retain the heat the temperature drops during the night to
minus -173 oC.
• Mercury’s orbit is inclined by 7° to the plane of Earth’s orbit (the ecliptic), as shown in
the diagram on the right.
Mercury
Mercury high density
suggests that like earth
suffered an impact
shortly after it went
differentiation. The
impact ejected much of
its mantle into space,
leaving a planet with a
large iron core. This
large impact would
have ejected most of its
water into space.
Mercury’s surface is flexed by
tidal bulges raised by the
Sun—the Sun’s tides on
Mercury are about 17 times
stronger than the Moon’s on
Earth.
Mercury is also among the least-habitable bodies in the solar system
because of lack of liquids and atmosphere.
Mercury
(Left) part of the enormous Caloris Basin. Probably
formed by a giant impact early in Mercury's history,
this basin was subsequently filled by lava flows.
Weird terrain at the antipodal point to the large Caloris
basin. The shock wave produced by the Caloris
impact was reflected and focused to the antipodal
point, breaking the crust it into a series of complex
blocks.
Mercury
Despite the generally extremely high temperature of its
surface, observations strongly suggest that ice exists
on Mercury.
Floors of deep craters near the poles are never exposed
to direct sunlight, and have temperatures lower than
the global average.
Water ice strongly reflects radar, and observations reveal
that there are patches of very high radar reflection
near the poles
The icy regions are believed to be covered to a depth of
only a few meters, and contain about 1014–1015 kg of
ice. By comparison, the Antarctic ice sheet on Earth
has a mass of about 4 x 1018 kg, and Mars’ south
polar cap contains about 1016 kg of water.
Two most likely sources of ice on Mercury are from
outgassing of water from the planet’s interior or
deposition by impacts of comets.
Even if Mercury has surface water, it will not be liquid
because its surface temperature are almost always
above the boiling point or far below the freezing
point.
Radar image of Mercury's north pole.
Mercury may have ices brought by
impacts in crater bottoms near its poles
that have not been exposed to Sun light
for billions of years.
Venus
Venus
Earth
Mass (MEarth)
0.8
1
Escape velocity (km/s) 10.4
11.2
Orbital semimajor
Axis (AU)
0.7
1
o
Orbital inclination ( ) 3.4
0
Orbital period (days) 224
365
Axial rotation (days) 243
0.997
o
Axial inclination ( )
177
23.5
Radius (km)
6052
6371
3
-3
Density (x10 kg m ) 5.2
5.51
-2
Surface gravity (m s ) 8.9
9.8
Mean surface T
733K (460C) 288K (15C)
Atmospheric surface
pressure (bar)
92
1
Atmosphere
CO2
N2, O2
Satellites
none
1
Highest point on
surface
Maxwell Montes Mt. Everest
(17 km above planetary radius) 8 km
Venus is the only planet which spins backwards.
Venus is completely cover by thick clouds of
sulfuric acid and other toxic chemicals.
Venus
The pressure on its surface is 92 times the one on Earth – equivalent of a depth of 1 km
in the ocean.
The planet Venus is often referred to as the Earth’s “sister planet” because it is almost
the same size and density.
With an Earth like atmosphere Venus global average temperature would be 35oC.
Venus has much higher temperatures and pressures than Earth.
Based on its distance from the Sun, we would expect the surface of Venus to be a little
hotter than the Earth. However the surface of Venus is much hotter than the Earth
because it has a very thick atmosphere of carbon dioxide – a greenhouse gas. Most
of the carbon dioxide on Venus is still present in the atmosphere, unlike on Earth
where most of the carbon dioxide on the Earth is dissolved in the oceans, forming
carbonate rocks. CO2 makes 96% of Venus atmosphere compared to less than 1%
for Earth.
Venus may have been more Earth-like in the past because the Sun was dimmer, putting
out less solar radiation.
Every planet in the solar system has strange and unexplained features. In the case of
Venus it's the spin. Venus is the only planet which spins backwards, all the others
move in the same direction as their orbit.
Map of Venus
Topographic Map of Venus from Pioneer Venus
Venus
False-color picture of Venus in ultraviolet light - acidic haze spread across Venus.
The unusual clouds were discovered last July by ESA's robotic Venus Express spacecraft currently
orbiting Venus. The bright haze is rich in sulfuric acid, created when an unknown process
lifted water vapor and sulphur dioxide from lower levels into Venus' upper atmosphere.
There, sunlight broke these molecules apart and some of them recombined into the volatile
sulfuric acid. Over the course of just a few days the acidic clouds spread from the South Pole
of Venus across half the planet.
Venus
The high surface temperature
rules out the possibility for
life at the surface.
The surface may have been
habitable in the past. Now
Venus lacks water and plate
tectonics to cycle carbon
dioxide. Crater counts suggest
that its entire surface is less
than one billion old, meaning
that volcanism or plate
tectonics reshaped it.
Radar image of Venus taken by
orbiting Magellan spacecraft
Venus
Landers sent to Venus lasted less than 2 hours before being disabled by high temperatures and corrosive
chemicals.
Actual photographs of Venus’s surface
Venus
Radar images: dark = smooth surface, light = rugged surface
Venus appears to be among the most geologically active planets in the solar system. Venus
Express is able to detect gases in the lower layers of the atmosphere and variations in its
temperature, possible signs of volcanic activity.
The large radar-dark areas are probably tectonically formed basins that have been filled in
by fluid lava flows, thus presenting a smooth surface to the Magellan radar system.
Image showing radio-thermal emission
(emissivity) of a volcano about 2 km high.
The hot surface of Venus shows clear signs
of ancient lava flows.
Three large impact craters with diameters
ranging from 37 km to 65 km
Venus
Computer generated three-dimensional perspective view of the surface of Venus from radar data
Venus
Radar image of large circular domes 25km across
Arachnoids are large structures of unknown origin that have been found only on the surface
of Venus. They resemble spider-webs - concentric ovals surrounded by a complex
network of fractures, and can span 200 kilometers.
Over 30 arachnoids have been identified on Venus, so far. The Arachnoid might be a strange
relative to the volcano, but possibly different arachnoids are formed by different
processes.
Venus
If in the past Venus had oceans and life arose,
microbes might still survive in the clouds . At
about 50 km altitude the greenhouse effect is
weaker and droplets contain liquid water.
The clouds are acidic, but their sulfur content
might provide chemical energy for
extremophiles to survive.
If life exists on Venus today, it will most likely
be found floating high in the atmosphere.
Movie - composed by six different sequences of
images obtained by the Venus Monitoring
Camera onboard Venus Express in May
2006, December 2006, and January 2007
respectively. Distance from the planet’s
surface varies from 60 000 to 25 000
kilometres. All images were obtained
through the camera’s UV filter, at a
wavelength of 367 nanometres.
Movie: Cosmos Disk 4. Ch. 8. [41-46:00]
Planet Venus (12 min)
Mars is a very important planet and we will speak about during the next two lectures.
Monday March 17th
Wednesday March 19 - Movie about manned spaceships to Mars - NOT ON THE WEB!
Exam questions from this movie!
Jovian planets
The four jovian planets are very
different from terrestrial planets.
- Massive, lower in density, composed
mostly of H, He and H compounds
(water, methane, ammonia)
- Observations and theoretical models
suggest they lack a solid surface
similar to the one of Earth.
Outer layers contain clouds of gaseous
H, He and H compounds. Deeper the
pressure increases and H and He are
in liquid form. In Jupiter and Saturn
the pressures are so high that H
becomes metallic.
They have cores of rocks, metals and H
compounds in very different phases
from those we know.
Jupiter
Jupiter
Earth
Mass (MEarth)
318
1
Escape velocity (km/s) 59.5
11.2
Orbital semimajor
Axis (AU)
5.2
1
Orbital inclination (o) 1.3
0
Orbital period
11.8 years
365 days
Axial rotation (days) 0.412
0.997
o
Axial inclination ( )
3.1
23.5
Radius (km)
70,000
6,371
3
-3
Density (x10 kg m ) 1.33
5.51
Surface gravity (m s-2) 23
9.8
Mean surface T
288K (15C)
Cloud top T
120K (-153C)
T at 1 bar pressure 165K (-108C)
Rings
few
0
Satellites
> 39
1
Atmosphere
H2, He, (CH4) N2, O2
Temperatures in upper atmosphere are very low, however they increase towards their deep interiors.
At some altitude the atmosphere is hot enough for liquid water to exist! Movie - Jupiter1.mp4
Jupiter
Storms and lightning on Jupiter = energy for life?
Movie - Jupiter2.mp4
Jupiter
Jupiter
Temperature far below freezing at
the cloud top, and increases with
depth.
Jupiter has several cloud layers,
each formed as different type of
gases condense.
Clouds containing water can
form at a depth of a little over
100 km (1% down from the
highest cloud).
Jupiter might host life in the
clouds!
The main impediment for life on
Jupiter is strong vertical winds
that would carry away organic
molecules at depth at which the
heat would destroy them. Life
with some sort of buoyancy might
stabilize it at a comfortable
altitude.
Movie. Cosmos Ch. 11. [53:0056:00] Alien life on Jupiter (3
min)
Jupiter
Could life survive on Jupiter
if it were to arrive from
somewhere else?
Probably not.
Jupiter has a strong magnetic
field. Jupiter’s aurorae are not
due to solar winds, but
probably to one of its
satellites - Io.
Io's volcanoes release
particles, some of which
become ionized and trapped
by Jupiter's magnetic field.
Saturn
Saturn
Earth
Mass (MEarth)
95
1
Escape velocity (km/s) 35
11.2
Orbital semimajor
Axis (AU)
9.5
1
Orbital inclination (o) 2.5
0
Orbital period
29 years
365 days
Axial rotation (days) 0.44
0.997
o
Axial inclination ( )
26
23.5
Radius (km)
58,000
6,371
3
-3
Density (x10 kg m ) 0.69
5.51
Surface gravity (m s-2) 9
9.8
Mean surface T
288K (15C)
Cloud top T
89K (-184C)
T at 1 bar pressure 135K (-138C)
Rings
many
Satellites
> 30
1
Atmosphere
H2, He, (CH4) N2, O2
Saturn
In the shadow if Saturn
The night side of Saturn is seen to be partly lit by light reflected from its own ring system.
Saturn
Movie. SaturnRingsCrossing
Saturn
Saturn
Saturn
•
Saturn`s North Pole. The bizarre hexagonal cloud pattern show stability even 20
years after Voyager. Movies of Saturn North`s pole show the cloud structure
maintaining its structure while rotating. Movie. SaturnPole
Saturn
•
•
•
•
•
At the South Pole lies a huge vortex
that is a hurricane-like storm, showing
no signs of dissipating.
The storm is slightly larger than the
entire Earth and carries winds of 550
km per hour, twice the velocity of a
category 5 hurricane.
Saturn is very similar to Jupiter that
the same considerations regarding
possible life should apply to it as well.
The biggest obstacle to life being
present in the atmospheres of Saturn is
the strong vertical wind speeds that
would rapidly carry organisms into the
hot.
In order for life to survive in the
atmospheres of Saturn it must be large
and buoyant, allowing it to maintain a
stable altitude in the atmosphere.
Uranus and Neptune
Uranus
Neptune
Earth
Mass (MEarth)
14
17
1
Escape velocity (km/s) 21
23
11.2
Orbital semimajor
Axis (AU)
19
30
1
Orbital inclination (o) 0.8
1.8
0
Orbital period
83 yr
163 yr
365 days
Axial rotation (days) 0.7
0.6
0.997
o
Axial inclination ( )
97
29
23.5
Radius (km)
25,360
24,620
6,371
3
-3
Density (x10 kg m ) 1.3
1.6
5.51
Surface gravity (m s-2) 8.7
11
9.8
Mean surface T
288K (15C)
Cloud top T
53K (-220C) 54K (-219C)
T at 1 bar pressure 75K (-198C) 70K (-203C)
Rings
several
few
Satellites
> 21
>8
1
Atmosphere
H2, He
H2, He
N2, O2
If life exists in Uranus and Neptune, it will most likely be
found in the oceans of liquid ices beneath the surface.
Movie. Uranusmagnetic. Movie. Neptunespot
Uranus and Neptune
•
•
Uranus and Neptude magnetic dipole
are off center by 30% of planet’s
radius.
One hypothesis is that, unlike the
magnetic fields of the terrestrial and
gas giant planets, which are
generated within their cores, the ice
giants' magnetic fields are generated
by motion at relatively shallow
depths, for instance, in the
water–ammonia ocean.
Uranus and Neptune
Uranus and Neptune are unlikely candidates for
habitability, same as Jupiter and Saturn.
They have colder atmospheres due to higher distance from
the Sun.
Vertical winds would make life unlikely.
However Uranus and Neptune might have a habitable zone
deep within their outer cores of water, methane and
ammonia, forming some very odd oceans.
At present we lack technology that would make the search
for this life possible.
Life on Jovian moons
•
Life on Jovian Moons will be discussed in a following lecture.
Spacecraft exploration of the Solar System
Information on the world in our solar
system comes from telescopic
observations, and spacecraft
exploration - manned or robotic.
Robotic missions comprise:
1. Flyby - a spacecraft goes past a world
just once and then continues on its way
2. Orbiter - orbits the world that it studies,
allowing longer term observations
3. Lander or probe - are landing on the
surface or probe the planet’s
atmosphere by flying through it. Some
landers can carry rovers to explore
wider regions.
4. Sample return mission
Spacecraft exploration of the Solar System
Flyby - cheaper because of lower weight
- cost of fuel. In addition to detailed
images they carry instruments to
measure magnetic fields, provide
info on masses, densities, sample
dust.
Orbiters - can study a world for a much
longer time than a flyby. Carry
cameras, spectrographs, radar for
precise altitude measurements. Is
more expensive than a flyby.
Trajectory of Voyager 2, which made flybys
of each f the 4 jovian planets.
Asteroid Eros photographed by NEAR spacecraft
that landed on Eros after orbiting it for a year.
Spacecraft exploration of the Solar System
Landers and probes
Galileo spacecraft 1995 dropped a probe into Jupiter’s atmosphere - collected temperature,
pressure, composition data for about one hour of descent
Cassini spacecraft carried a probe - Huygens - descended on Saturn’s moon Titan
Rovers on Mars - Spirit and Opportunity
Spirit and opportunity landing on Mars. Artist’s conception
Next lecture
Searching for life in our Solar System- Mars