Enigmatic New World Discovered Orbiting Young Star

CVSO30_System
Planet ‘c’ of the CVSO-30 system is a newly discovered substellar object, imaged by the European Southern Observatory’s Very Large Telescope (VLT) atop Paranal. Click image for larger, full-res view.

In a recent article we described a newly discovered, relatively close planetary system hosting 3 earth-class planets in orbit around an ultra-cool red dwarf star. That star’s mass was just above the stellar mass threshold for it to sustain hydrogen fusion reactions in its core, or Hydrogen Burning Mass limit, the threshold below which internal gravitational heating is insufficient for commencement of sustained nuclear fusion reactions.

In a March 17, 2016 study published in the journal Astronomy and Astrophysics and just released, another new and enigmatic world has been discovered in orbit around its host proto-star, this time using the “direct imaging” method of exoplanet detection. This technique is particularly effective for planets on wide orbits around young stars, such as the CSVO-30 system, since the light from the host star doesn’t overwhelm the feeble light from the planet and is thus, easier to detect. A collaboration of astronomers working with the Keck Observatory’s twin 10 meter telescopes on Mauna Kea, the European Southern Observatory’s 8 meter Very Large Telescope array at Paranal, atop the Chilean Atacama high desert plateau, and the Calar Alto Observatory facilities in Spain, have produced a comprehensive study of CVSO-30c, the second planet in the CVSO-30 system. If confirmed (and in all likelihood it will be), this would be the first system with a very close planet, discovered using the transit method such as is used with the Kepler Orbiting Space Telescope and the TRAPPIST system and a very distant planet, discovered using direct imaging. With a mass of 4 Jupiters CVSO-30b, the very close planet orbiting at 0.008 AU, was discovered in 2012 using the transit method. Regarding the discovery of CVSO-30c, representative astronomers were quoted as saying that this study describes, for the first time,:

“the  direct  detection  of  a  wide  separation  directly imaged planet [candidate] around a star (CVSO 30) which also  hosts  a  short  period  transiting  planet  [candidate].”

They went on to state that we

“are still exploring how such an exotic system came to form in such a short timeframe, as the star is only 2.5 million years old; it is possible that the two planets interacted at some point in the past, scattering off one another and settling in their current extreme orbits.”

CVSO-30_Location
A circle indicates the location of the CVSO-30 system in Orion. This image, produced with Stellarium using today’s date, shows the placement of the sun in relation to Orion and thus, the system. Click image for larger, full-res view.

Located in Orion at a distance of 1,200 light years, the system is so young that the host star, CVSO-30, on track to become another M-class red dwarf star such as TRAPPIST-1, is still in its T-Tauri stage of evolution. The T-Tauri stage of any star’s evolutionary track is the last stage of its formative phases before which the star is considered a “normal” or Main Sequence star, the point where gravity is balanced by outward gas pressure from the ongoing hydrogen fusion reactions in the stellar core. During this phase, the star exhibits a fierce stellar wind, dispersing all material left over from its formation, foreclosing the possibility of any additional planetary formation. If planets are going to form around any new star, this must occur before the onset of the T-Tauri phase. Thus, all planetary formation in the CVSO-30 system has ceased, limiting it to the two planets CVSO-30b and CVSO-30c.

In its current evolutionary state, CVSO-30 hasn’t stabilized and is still contracting in size and converging in luminosity towards what will ultimately be its “zero age main sequence” point, the point on the stellar evolutionary diagram known as the Hertzprung-Russell diagram where the star will remain for its entire productive life. Although its mass will remain stable, within 5% of where it is now at 0.39 (39%) solar, its luminosity will change significantly, dropping from its current value of 0.25 (25%) solar to about 10% of that value or about 2.5% solar. In the illustration below, it is instructive to note the migration and evolution of the habitable zone as the star stabilizes and converges towards its main sequence state. As it is now, its on track to become an M3-V red dwarf, an “early” (“hotter”) M class star. The numeric designation within stellar class (1, 3, 5, etc.) decreases with increasing effective temperature, i.e. an M1-V star is hotter than an M3-V star. Although this star will be towards the hotter end of the range within class (M), it will still be quite cool and diminutive in terms of luminosity compared to stars such as the sun.

At 4.7 Jupiter masses, the newly discovered object, CVSO-30c, has a mass of 1 part in 3,000 of the hydrogen burning mass limit and is  considered substellar, below the threshold of what would be considered a “Brown Dwarf” at 13 Jupiter masses. That does not mean to say that it doesn’t produce its own heat and energy. It exhibits a measured effective temperature of 1,600 K (1,327 C) and a luminosity of 1.6596E-04 solar (1 part in 6,000 of the sun’s luminosity). Brown dwarfs and very low-mass substellar objects such as Jupiter (Jupiter emits 3x the Infrared energy it receives from the sun), produce energy through gravitational heating, the same process that is the preceding catalyst for sustained hydrogen fusion reactions in stars above the hydrogen burning mass limit.

At 660 AU (1 Astronomical Unit is the Earth-sun distance) from its host star, CVSO-30c has an orbital period of 27,000 years and receives virtually no heat or energy from the host star whereas CVSO-30b is roasting at 0.008 AU (1,200,000 Km or less than 4x the distance to the moon) with an effective nominal temperature of 3,120 Kelvin (2,847 C), an 11 hour orbital period and a 208 Km/sec orbital velocity!

It is instructive to compare the TRAPPIST-1 and CVSO-30 systems alongside the sun and our solar system’s inner planetary environment.

TRAPPIST-1_v_Sun(final)
This diagram compares three planetary systems and their host stars side by side, the TRAPPIST-1, the CVSO-30 systems and our own sun and solar system. As a comparison and reference, the prominent summer star Altair at almost eleven solar luminosities and the bright winter star Procyon are also included. The left-hand column lists the 3 systems with their planets’ respective distances from the host star, the middle columns list and compare the prevailing temperatures due to host star irradiance (heat and light) at the respective planetary distances from the host star. Included in the first column are the locations (distances from host star) and extent of the respective habitable zones. The HZ comparison section of the chart is delineated below the planetary system comparisons. The table is color coded, with light red background and red text indicating a temperature high and outside of the very narrow range where water can exist in a liquid state, green indicates the temperature falls within that range and blue background with white text indicates the temperature is below and outside of that range. For reference, the freezing and boiling points of water expressed in Kelvin are listed along with the luminosities of the two extra-solar host stars and the sun’s nominal power output in Watts. It is instructive to note the migration and evolution of the habitable zone as CVSO-30 stabilizes and converges towards its main sequence state. Click the image for an expanded view.
HZ_Extent_vs_StellarLuminosity(final)
Using data from the 3 planetary systems and the reference stars Procyon and Altair, this diagram establishes an empirical power law between Habitable Zone extent (in AU) and stellar luminosity (sun = 1). As indicated by the model curve function, the HZ extent varies as the 1/2 power (square root) of the Stellar Luminosity. Click the image for an expanded view.

Its interesting to note how the various planets compare in terms of the prevailing temperatures at their respective distances from their host stars and what those conditions would be in each of the respective systems and how the host star’s luminosity plays a large role in determining the overall planetary environment for each of the systems. It is also instructive to note how the habitable zone scales in location and extent with host star luminosity. Take particular note of the prevailing temperatures at CVSO-30b and CVSO-30c, the planets of the newly discovered CVSO-30 system. The temperatures fall way outside of the narrow range of temperatures where water can exist in a liquid state, precluding the possibility of life ever evolving in that system, the planet’s actual properties notwithstanding -its a gas giant with a mass of about 5 Jupiters and a self-emissive effective temperature of 1,600 K. The prevailing temperature at CVSO-30c is barely 11 K, eleven degrees above absolute zero! If replaced with TRAPPIST-1 as the host star, the prevailing temperate drops to 2 K, two degrees above absolute zero (as a reference, Helium boils -changes phase from liquid to gas- at 4.3 K and freezes at 0.95 K)! Even if replaced with the sun as the host star, the temperature is still a frigid 15 K!


Imagination is more important than knowledge 585px-Albert_Einstein_signature_1934(invert)
An index of all articles in this blog can be found here.

 

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6 thoughts on “Enigmatic New World Discovered Orbiting Young Star

  1. Do you have UPDATED information on the orbit of TRAPPIST-1d? The discovery paper stated that it could have any one of twelve different orbits, with the highest probability of an orbital period of 18.2 days. Your illustration indicates an orbital separation of 0.030AU. Does THAT correspond to an 18.2 day orbital period?

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    1. Thanks for the reply, Harry. The short answer to your question is no, the period for an orbital radius of 0.030 AU corresponds to 6.72 days. The study suggests that the two inner planets are in the habitable zone: “….placing them close to the inner edge of the habitable zone of the star”. Radiation theory (from which the chart is based) places them well inside the habitable zone with the only planet likely to be in the habitable zone being planet 1d. The 0.030 orbital radius was chosen (as explained in the article) for two reasons: it was within the distribution of possible orbital radii and was also within the star’s habitable zone. This star’s habitable zone is very narrow and thus, even a modest increase in the orbital radius places the planet well outside the HZ. I have since updated both articles with expanded explanations as well as updated charts and illustrations. I should point out while we’re discussing the orbit of this planet, the authors make an unqualified reference to the planet’s ‘circular’ orbit. In point of fact, there are no perfectly circular orbits in nature due to mutual gravitational effects of all bodies in a particular system.

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  2. Thank you both for your thoughtful comments. I have updated this article and associated diagrams to reflect additional results and insights from the ongoing investigation.

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