Students from Lancaster, Pennsylvania have been following the
Planetary Lake Lander, and wrote in a lot of very good questions about
what the project.
These questions were answered by Dr. Nathalie Cabrol, the Principal
Investigator for the Planetary Lake Lander Project, and Dr. Ellen
Stofan, the Principal Investigator for the Titan Mare Explorer (TiME)
mission that was proposed to NASA last year. Dr. Cabrol, an
astrobiologist, and Dr. Stofan, a planetary geologist, are both
scientists who study the surfaces of Earth and other planets in order
to understand the physical processes, such as glaciation, volcanism
and erosion, that shape planetary surfaces over time and lead to the
development of possible habitats for life .
Q. What kind of life may be possible on Titan/Saturn/Mars? Why is NASA
(and why are you) so interested in Titan? Is NASA’s assumption that
there may have been an ecosystem on Mars or Titan before the glaciers
melted? How do we know there were glaciers? How do we know that
conditions on Mars or Titan resemble conditions in the deglaciated
lake in the Andes?
A. We know that comets and asteroids have delivered the carbon
compounds or building blocks of life all over the solar system.
Astrobiologists believe that life requires water, a source of energy
(like lightning or volcanism) and nutrients. Life on Saturn, with its
high pressure and hydrogen gas atmosphere is not like any habitable
environment that we know of! However, science fiction writers have
thought of organisms that could live off lightning floating in the
clouds! At Titan, there is no liquid water and it is very, very cold.
However, there are liquid hydrocarbons (sort of like oil or gasoline)
and there is much about the evolution of life here on Earth, let alone
on other planets, that we would learn from exploring the undoubtedly
complex organic chemistry in Titan’s lakes. Titan can be thought of as
having conditions similar to those of Earth when life evolved, only
Mars was very similar to Earth for a short period of time, with liquid
water on its surface, so life is likely to have evolved. But since the
time period was short, life is likely to be microbial.
There are no glaciers on Titan- its cold climate has been stable for a
long period of time. High-resolution orbital imagery of Mars has
revealed evidence of glaciers on its surface- the youngest are likely
500,000 years old. We know these glaciers must have gone through
periods of melting and sublimation. Some of this glacial ice may be
preserved under layers of debris. This ice may still harbor microbial
life, so they would be excellent targets for a future Mars mission!
The lake in the Andes is being used to test technology to explore
lakes on Titan, while the conditions in the deglaciating lake may be
similar to those at some point in Mars’ past. And of course, they are
also helping us to understand the effects of our warming climate on
ecosystems here on Earth.
Q. What specific types of things would you have the rovers look for
that would help you draw conclusions about the possibility of life?
How can you make the rover determine what is of ‘interest’? What does
your team consider to be something of interest that you would want it
to capture? What specific experiments are you conducting that are
helping you to better understand the conditions on Mars? Will the
rover be doing chemical/spectroscopic analysis? What tests do you do
for a search for life so far away? What do you expect to find?
A. Rovers to Mars carry instruments to measure the chemistry of the
surface and atmosphere, looking for the building blocks of life- like
complex organic compounds that are present in life here on Earth.
Because we are working in an analogue environment to Mars, we are
learning to recognize the signatures that indicate life—which will
help guide future exploration of Mars and Titan. In Titan’s lakes, we
would also measure the organic content of the lake liquids. Tests for
life are both direct- a fish swimming by- as well as indirect-
measuring a compound that is being ‘eaten’ or depleted by some form of
life, resulting in that organism then expelling, or producing an
excess, of some other compound. For example, cyanobacteria absorb CO2
from the atmosphere, and then precipitate solid carbonate structures.
Other organic activity can produce methane gas, which can also be
detected easily in an atmosphere.
Q. What were the major setbacks (if any) in designing the rovers you
currently have, and how long did it take to design them? What types of
improvements are you looking for? How do you prevent a lake lander
rover from floating? What is involved with the programming of a rover
(what methods/tools are involved in getting it to ‘think’ for itself)?
How do you communicate with it?
A. For rovers, we looked at the science questions and the hypotheses
we want to test, and we design a science payload around those
questions. Each mission has a specific scientific goal, which then
govern what it needs to do- for example, how far it needs to go and
how it needs to make measurements. Rovers do have setbacks, for
example, of the two Mars Exploration Rovers, only Opportunity is still
operating as Spirit got stuck in sand. In addition, some mechanical
parts have trouble over time with the very cold temperatures on Mars.
For Titan, our job is easy, as we actually want to make most of the
same measurements we make at lakes and seas here on Earth—which then
in turn drives the design. To make sure we will float, we look at the
chemical nature of the likely lake liquids, for Titan methane and
ethane instead of water, and design the lake lander to be buoyant in
To get a rover or lake lander to think for itself, we are trying to
teach them to understand their environment. You do this by having them
collect data, and then analyze it- looking for trends, and then
deviations from what is normal. For example, for measuring wave
conditions on a Titan sea, a lake lander may change how often it is
collecting data if it senses that it is suddenly bobbing more than it
To communicate with rovers or lake landers, we type lines of codes to
command them, and then send these new instructions via the Deep Space
Network- a set of antennas around the world that are used to
communicate with distant spacecraft. Every lander has an onboard
antenna system and computer, which is programmed to receive commands
and update its operations. It then in turn, has the ability to send
data back to the Earth via the Deep Space Network.
Q. Now that ice has been found on Mercury, will more attention be
given to exploring Mercury (instead of Mars)?
A. The discovery of ice at the poles of Mercury by the MESSENGER
spacecraft is very exciting. We know that some of the ice was brought
there by comets impacting Mercury, and so analyzing it would give us
information on some of the basic materials that were also brought to
Earth early in its history. Hopefully there will be follow on missions
to Mercury, but Mars remains an important place to explore, as we know
that Mars had liquid water on its surface for some length of
time—conditions which may have been conducive to life. Also, Mars is
best suited for human exploration, as Mercury experiences huge
extremes in temperature being so close to the Sun.
Q. How do ecosystems change when glaciers melt?
A. One example is that when glaciers melt, they bring a lot of
sediments and nutrients into a lake that makes the water milky, or
turbid, but those nutrients also provide what life in the lake needs.
As time goes by, there is less ice to melt, so less discharge from the
glacier, less power of transport, so less sediment and nutrients come
into the lake. The sediment settles at the bottom of the lake, making
the water clearer, but less healthy for the organisms that live there.
Sunlight can now reach deeper into the lake, which may harm some
organisms living in the lake. They may now be replaced by a different
set of organisms or they may have to move to deeper depths. The result
is generally less diversity of life in the lake. In the last phase,
very little new material is being brought into the lake, which has
become a closed system, so organisms now have to seek nutrients from
near shore plant life or aerosols falling into the lake from the
atmosphere. If precipitation stops, the lake will eventually dry up,
and a totally new and different ecosystem results. Organisms that can
adapt to changing environments will survive, while less tolerant
organisms will disappear.