Greetings from Palmia Observatory
Hooray, this week we finally received our 2nd vaccine shot. Resident Astronomer Peggy will get her 2nd shot next week. In the meantime, we watched some great video of Perseverance landing on Mars and sat in on the online AAS Habitable Worlds conference and can provide some brief comments.
First up, we received some web references for the Perseverance landing on Mars from Science Nerd & OCA, Scott, Math Wiz & OCA, Dave and Into Power, Richard. This short video shows some great images of the parachute opening and the thrusters disturbing the Martian soil as the craft lands. Thanks for that Scott ,Dave and Richard. You can check out the video at: https://www.youtube.com/watch?v=4czjS9h4Fpg&feature=youtu.be
Here you can see the open parachute when it is still possible to bleed off high entry kinetic energy in the thin Martian atmosphere.
|Parachute opening for Perseverance Rover's Descent and Touchdown on Mars (Source: NASA)|
Next, the Habitable Worlds 2021 online conference brought together presentations from a multidisciplinary group of scientists that included astronomers, planetary scientists and and astrobiologists, who discussed some of the measurements of exoplanets and biosignatures for life.
|Habitable Worlds 2021online conference, Feb 22-25 (Source: www.aas.org)|
One of the general lessons learned was how studying exoplanets and evaluating habitability requires a whole range of separate fields of study. This one slide, from a presentation by Francis Nimmo, shows how habitability depends on much more than just some distance from the home star and includes the effects of plate tectonics and magnetic fields how they all combine together with the atmospheric effects.
|Connecting the observations and importance of magnetic fields (Source: Francis Nimmo, Habitable Worlds 2021)|
The first measurements that affect the possible habitability are the temperature measurements. It is hard enough to detect an exoplanet around another star and this detection provides the first means of measuring the planet's temperature.
|Phase measurements of exoplanet temperatures (Source: Eric Wolf, Habitable Worlds 2021)|
Planetary scientists want to develop Global Circulation Models (GCM) to include the effects of oceans, if any, and continents and wind patterns, but that type of analysis is pretty difficult on exoplanets and so the phase curves of temperature are still a key data point.
|Use phase curves and do Global Climate Modeling later (Source: Eric Wolf, Habitable Worlds 2021)|
Amy Glazier presented an interesting technique to look for exo-auroras, that is auroras around the exoplanet, as a way to determine the characteristics of the atmosphere. The method relies on storms, flares and CMEs from the home start to excite the gases in the exoplanet atmosphere. Observing the spectra of the auroral light indicates what chemicals are in the atmosphere.
|Using exo-aurorae to study exo-atmospheres (Source: Amy Glazier, Habitable Worlds 2021)|
To detect the spectra from these exo-auroras requires a large aperture telescope with a good spectrometer such as the Southern Astrophysical Research (SOAR) Telescope in Cerro Pachon, Chile.
|Using SOAR to get exo-aurora spectra(Source: Amy Glazier, Habitable Worlds 2021)|
The exo-aurora can be very dim and it takes a big scope and long spectra data collection periods. In order to effectively use the allocated time on the big scope, the plan is to use a smaller set of telescopes to identify when a particular exoplanet host star has generated a solar flare type event. Then, within a day or two, the effects of the flare on the exoplanet atmosphere, will result in an aurora event. So, the Evryscope Fast Transient Engine (EFTE) is used to identify transient candidates for rapid follow up with the large telescope spectrometer.
|Using EFTE to identify targets for aurora spectra(Source: Amy Glazier, Habitable Worlds 2021)|
The data for EFTE is provided by the Evryscope-South telescope which uses 22 cameras to generate a whole sky picture of possible flare events.
|Scan the skies for flares that can excite exo-aurora (Source: Amy Glazier, Habitable Worlds 2021)|
There is growing interest in planets around M-dwarf stars. There are a lot of M-dwarfs and the exoplanets can be located quite close to the star because it is much dimmer and cooler than less common stars like our sun. But, M-dwarf stars are found to be very energetic and through off a lot of flares and CMEs, especially when they are young. This behavior is thought to result in high radiation at the exoplanet, which can result in atmospheric loss, including much of the water. Keavin Moore went into some of the details of the loss mechanisms.
|Will planets around M-dwarf stars be desiccated? (Source: Keavin Moore, Habitable Worlds 2021)|
A planet is not likely to be habitable, if it does have the right temperature and size to support liquid water on the surface, if the active M-dwarf star causes all the water to be blown off the planet.
|Water loss mechanisms on exoplanets (Source: Keavin Moore, Habitable Worlds 2021)|
Keavin then explained some of the water loss mechanisms and how water stored internally to the planet can be brought to the surface by tectonic processes. Again, this shows the relationship between an active exoplanet that is a live and supports tectonics also with a convective molten core that supports a magnetic field. The magnetic field can help deflect some of the solar wind and thereby minimize one of the major sources of loss of atmosphere.
|Water storage reservoirs are the key to maintain water (Source: Keavin Moore, Habitable Worlds 2021)|
Fortunately, there is a possible way out of having an exoplanet, like an M-Earth, from being desiccated by the M-dwarfs flaring. It turns out that if the exoplanet has plate tectonics and if the age of the M-dwarf has resulted in it slowing down the amount of flaring, that water from deep within the planet's mantle can be brought to the surface and maintain water on the surface. Hmm, I hope this hypothesis proves out to be valid.
|Hide the water on M-dwarf planets until later recovery (Source: Keavin Moore, Habitable Worlds 2021)|
Another condition for habitability and determining if an exoplanet could support life or had life at one time is its elemental composition. It is hard to measure the chemical composition of the exoplanet remotely but the elements in its sun, because the planet formed out of the same gas that formed the star, are used as an indicator of possible composition of the planet. Now there is a lot of geophysics and geology that goes into the differentiation and layering of chemical elements that make up the core and mantel, but if the right elements are found in the star, then there is reason to expect the same elements on the planet.
Here Natalie Hinkel discusses the fairly fixed stoichiometry associated with photosynthesis. Now it is an open question if this same story of chemical photosynthesis applies to the exoplanet, but at least if we find the same types of elemental chemicals there, then we have good reason to say that life might be possible. She showed how photosynthesis is found on Earth to follow a general rule of requiring 106 carbon atoms, 16 nitrogen atoms, 122 water molecules and one lonely phosphorus atom to achieve the right stoichiometry. Of course, there is not guarantee that this type of photosynthesis is going on there.
|Planetary chemical composition and life (Source: Natalie Hinkel, Habitable Worlds 2021)|
But, an examination of the Hypatia catalog, which tracks many nearby stars, shows that there are many stars that could provide their exoplanets with the required amounts of these chemical elements.
|Hypatia catalog tracks stars and chemical composition (Source: Natalie Hinkel, Habitable Worlds 2021)|
So in summary, we can see in just these brief comments how the habitability of exoplanets is being explored and how a multidisciplinary approach is required to investigate the many attributes of habitability, not just being the right distance away from the star.
Until next time, here from our burrow, stay safe, as we recover more of our freedom,