The slight variations we’ve observed in the past occur on scales so slow and minute that they pale in comparison to current rates. This goes back two ticks on the next graph (Petit, et al., 1999). These changes may be small, but they are significant.
The climate is changing dangerously fast.We can begin to work towards fixing it, or we can set us down a very dangerous path. And we can change it; the mere fact that we are warming the earth so quickly shows just what we are capable of.
Well, this is embarrassing. This is not what I had planned to discuss this week. This is the point where I go over the different test cases I’ll be using Tekton on. Unfortunately, my time has been almost entirely monopolized by my attempts to prepare a lab for the Astrobiology Class. The lab is done. The trouble has been with the results I keep getting which are slightly off from what all the published literature is saying. After much review, I think I’ve figured out the issue which relates to over-saturation of the main (higher sensitive) sensor. So it wasn’t all for not, but given the amount of time its taken me, I think its worth something discussing so we can all get a better idea of how to deal with other types of data sets, especially non image ones.
Cassini-Huygens is an unmanned spacecraft sent to the Saturnian system. Since its arrival in 2004, it has provided many discoveries that have fundamentally changed the course of future planetary exploration. With its many moons and rings, many consider Saturn to be like a mini solar system.
The Cassini-Huygens Spacecraft is made up of two main components: the Cassini Orbiter and the Huygens Probe. The orbiter hosts a range of science instruments in:
Optical Remote Sensing: used to study Saturn, the rings, and moons in visual and infrared wavelengths.
Fields, Particles, and Waves: used to study the dust, plasma, and magnetic fields around Saturn and its moons.
Microwave Remote Sensing: uses radio waves to map atmospheres, determine mass of moons, and collect data on the rings. It also unveils details about the surface of Titan.
The Huygens probe hosted its own set of instruments to more closely study Titan.
Ion and Neutral Mass Spectrometer (INMS)
INMS characterizes the neutrally charged particles and low energy ions in the gases in Titan’s atmosphere, Saturn’s magnetosphere, and the ring environment to determine their chemical, elemental, and isotopic compositions (Fig. 1).
The instrument counts the number of particles present. These counts are converted to a specific density of particles in a region for a range of masses from 10 to 100 Daltons (the atomic mass per elemental charge). These correlate with specific compounds by their molecular weights, thereby revealing the abundances of each.
Ion measurements are done in two modes: open source and closed source (Fig. 2). The closed source mode is used to measure non-reactive neutrals such as CH4 and Nitrogen. Open source mode measures positive ion species which tend to be less abundant. If you’re interested in identifying neutrals, the best route is to filter out the open sourced data, but this will impede your ability to study both ions in the spectrum. This allows for separating neutrally charged species from the charged ion species. Closed source increases the pressure of the incoming species to help facilitate readings. However, reactive species would react with instrument walls and thus require a different approach.
Calibrations and Sensitivities of INMS Data
Each species (mass value) must be calibrated to account for instrument sensitivities and other factors. These factors vary for each species, so it requires a close analysis of each potential species. A sensitivity factor, of units counts/s/cm3, varies for each potential species measured. These are listed in a calibration file on the Planetary Data System (PDS) website. The results are also effected by the angle and velocity of the spacecraft and is accounted for using the Ram enhancement factor, which is unitless. It’s dependent on several factors: the velocity of the spacecraft relative to the target (e.g. Titan), the angle of the INMS aperture ( theta), the temperature of the air (Ta ) and the instrument (Ti ), as well as the mass of the molecule (m) being considered. Then density, , can then be ascertained,
where N is the number of counts that the instrument measures and tIP is the instrument integration period (0.031032 seconds). Needless to say, converting the raw data to physical number is a long and complex process. However, we will be circumventing the calibration process and calculating the results for the three known major species: hydrogen, methane, and nitrogen. The Sensitivity and Ram enhancement factor are shown in Table 1.
There are two sensors on the INMS instrument. One is a high sensitivity sensor and the other is low. The high sensitivity works such that as it approaches saturation, the counts become throttled. This begins being significant after 40,000 counts. When it becomes completely saturated, the high sensitivity counter goes to 0. In order to get an accurate reading, you have to design a method that uses both counters, following these rules:
where C1 represents the first column of counts (high sensitivity) and C2 represents the second column of counts (low sensitivity). If the high sensitivity response is completely saturated, C2 will be much higher. Occasional readings may give 0 and 1 for C1 and C2, but these are still false and need to be filtered out. To be extra cautious, we choose values higher than 12 because the sensor becomes unreliable below this point.
Another issue associated with saturation is dead time, where the receiver is overloaded with so many points that the detector misses some point as it lags in a way. However, this barely produces a 20% lag for even 20,000 counts, well above the highest counts we will deal with. For that reason, we will not worry about this correction.
Lastly, during closest approach, CASSINI begins to enter Titan’s atmosphere. Drag slows the spacecraft down, so thrusters must be used to maintain velocity. The exhaust includes high quantities of hydrogen, which can contaminate the hydrogen (2 Daltons) counts. You will be dealing with a flyby where this effect is minimal, but it is important to be aware that it may skew your results slightly.
Titan is the only moon in the solar system with a thick atmosphere. Nitrogen is the dominant species in the atmosphere, with a few percent methane present. Other components have been suggested based on a mix of ground studies and Voyager and Cassini observations.
The major constituents that were expected to be found in Titan’s atmosphere are shown in Table 1. Solar UV radiation and energetic particles interact with Titan’s atmosphere, ionizing and dissociating compounds. Over time, the most abundant constituents (methane and nitrogen) combine to form larger compounds. This is visualized in Figure 3.
Saturn has many icy moons other than Titan. Enceladus stands out because it is well known for its huge plumes of water emanating from the tiger stripes in the south pole. The ocean extends under the entire ice shell but is likely largest in the south pole. Its close proximity to Titan could prove hopeful for potential mixing of compounds between the two worlds.
PDS: The Planetary Data System
The Planetary Data System is an archive of all the public scientific data from NASA planetary missions, astronomical observations, and laboratory measurements. It offers several ways of browsing data whether by the body of interest, a particular mission, or by specific fields of science. We will navigate using the PDS Nodes which are located on the left side of the PDS home page. The nodes are broken down by area of research as follows:
Atmospheres: specializes in non-imaging atmospheric data from all non-earth missions.
Geosciences: specializes in data related to the study of surfaces and interiors of terrestrial planetary bodies.
Cartography and Imaging Sciences: specializes in all the digital image collections from past, present and future planetary missions.
Navigational & Ancillary Information (NAIF): specializes primarily in engineering related information such as system navigation and other mission functions.
Planetary Plasma Interactions: specializes in data related to solar wind, magnetospheres, ionospheres and their interactions with planetary atmospheres and surfaces.
Ring-Moon Systems: specializes in all data related to planetary ring systems.
Small Bodies: specializes in data related to asteroids, comets, and interplanetary dust.
There are a lot of other ways of navigating the site, and this is just one way of trying to find what you have.
OPAG: the Outer Planetary Assessment Group meeting
OPAG was a very different experience from my past conference experiences. The focus on current and potential missions and the the technicalities that go along with them, was very interesting to see. There were several different projects that I’ve heard about that it really helped me understand there standing.
Take LUVOIR (the Large Ultraviolet/Optical/Infrared Surveyor) . Some have gone so far as to call it the successor to Hubble (GASP!). This is something Britney has mentioned and discussed with her group at GA Tech several times. I never quite understood where that stood. Turns out its a mission concept in the making with an estimated 2030 launch., and while it isn’t the only option, I think it has a really good chance of succeeding. Usually, OPAG is about missions involve the outer planets. LUVOIR is more of an astronomical project, but it’s unique because the designers recognize, and are taking full advantage of the fact, that it has a wide array of applications in planetary science.
Its aperture will be between 8 and 16 m, compared to Hubbles 2.4 m (JWST 6.5 m). Also unlike Hubble, it will be serviceable and up-gradable for decades. At 1000 AU, the distance of the hypothesized 9th planet, Hubble would see it as a complete blur. LUVOIR wouldn’t see it in full detail, but would see it about as well as Hubble saw plut (qualitatively speakiing). Remember Pluto is ~30 AU. It could make out Earth and Venus and Jupiter size planets of systems 13 parsecs away. Could make out the surfaces of IO and Europa, enough to track changes, and it could distinguish the heart on Pluto.
The plan is to come after JWST, but it also sees farther and with a wider range of view (spectraly) than the JWST. It has its problems and limitation but compared to the other missions being proposed, I think it’s the best being proposed. There is a far infrared, an x-ray, and an exoplanet observer. I think LUVOIR is best because offers the wides range of opportunities. It will provide insight into Astrophysics, Cosmic origins, our solar system, and exoplanets.
Other news involved an update on The Europa Clipper. This wasn’t an introduction but more of an update, so it was more difficult for me to follow along. It was largely about refining the instruments, their capabilities, and the overall plan. The overarching synergetic sciences were as follows.
Gravity though doppler measurements
Magnetometry and plasma to confirm ocean and ice thickness
Infrared to understand composition and compounds on surface (especially to find organics)
Could help pave the way for future lander missions
RADAR to find subsurface waster (melt lens?)
Ultraviolet to detect vapors escaping surface
Gas and dust spec to understand what is escaping
Dragon Fly and potential New Frontiers Missions
There was a discussion of a few ideas involving a new New Frontiers Mission. There was an idea for the Enceladus Life finder (ELF). IT would investigate Enceladus’s ~100 jets, which is modulated by diurnal tidal flexing and is what feeds the E ring. It would search for composition (organic rich molecules sourced from the ocean) and do in situ detection of biomarkers (with a cosmic dust analyzer and NMS). It would study both gas and grains with an intent to undestand the evolution of volatiles (looking for finer scaled masses the INMS hasn’t been able to find, understanding which have reacted with water, and are they effected by hydrothermal vents), habitability (temp, redox energ, oxidation state, pH, etc.), and life (amino acides, membrane molecules, and isotopic trends) in the regions.
A long shot that was proposed more as a 2050 vision was the Pluto Orbiter. They focused less on the logistics and more on the potential science. Although, I thought it was premature.
Finally, the big reveal was the Dragon Fly Titan lander. They discuss it in a LPSC abstract if you’d like to read more about it. The true magic behind it is that it makes use of Titan’s thick atmosphere. It would be very similar to Mars missions, except it would use a helicopter like design to move between sites, unlike Mars landers and rovers ever could. The main objective is to understand the organic and methanogic cycle on Titan and how that relates to life. It seeks to understand the prebiotic chemistry and habitability by studying the complex organic material. Its an amazing laboratory because its an Earth like system with a methane cycle instead of water. We might find hydrocarbon based life, entirely different from our own. Think of all we could learn from this one lander as we can fly to specific regions with diverse surface materials. Other flight options include a hot air balloon, an airplane, etc. The challenge is to get a capable mission suit to high priority sites. The Dragonfly rotorcraft lander could travel to settings 10s to 100s km apart all while taking aerial imagery and atmospheric profiles.
The potential Europa Lander
As a concept, I think it’s a really cool idea. They released a nearly 300 page report (source of images provided). I know Catherine has serious reservations regarding this, and for good reason. All the same, I can’t escape the fondness I have for it or Europa. Catherine put the most recent cost estimate at $4B. A similar study in 2012 gave an estimate by an independent estimate at $3B. Whatever it may be, I think we can agree it is probably too high. It would overshadow other missions and allocate too many funds to this one task. That being said, the presenter (I think Kevin Hand) had a few things to say about it. One, clipper is in the works and would aid in selecting a site in the future, but more importantly, he says, we need to develop a mission capable of doing this type of science with limited information. As we venture further and further out, it will become increasingly difficult to do reconnaissance of the bodies we visit. It is advantageous to develop a system capable of handling and reacting to the given terrain. Now, I am not here to advocate for the Europa lander, but it’s big news in planetary science. In fact, they’re aiming for a 2024 timeline.
Even if you don’t like the idea, the science is still pretty awesome, and is applicable to other missions as well. The primary goal is searching for bio-signatures, then understanding habitability, then giving context by defining surface properties and planetary dynamics.
There is so much that can be said about this mission and the science. I think it’s worth exploring the report more if only to understand the type of science they would do and specifically how they might search for life. It is an amazing (and well illustrated) look at such a complex world and how we might come to understand it.
Update on research
I spoke to Zibi. We made progress on the code but still got an error. I am going to try it again with Michael Bland’s files, but in the mean time Zibi will try to understand the issue we are getting. After I explore Michael’s code I am going to delve more into the literature and develop the range of test cases we want to implement, with a plan to present these at Titan through Time.