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English GeoScience Café No.26

Generate:2018-12-26 17:36:34 Reader:[845]

Planets And Roche Limit Distance: Asteroid Disruption And Meteorites
Host: Muhammad Freeshah; Text: Shuo Shen; Photo: Uqba Ramzan; Video: Li Yong,Ahmed Reda; Reviewer: Shanhong Liu, Steve McClure

About the speaker
Voropaev Sergey graduated from the physics department of Moscow State
University (M. W. Lomonosow) in 1987, specializing in Theoretical Physics. He wrotehis PhD thesis on mathematical and quantum physics in the department of theoretical physics, Moscow State University (M. V. Lo -monosov), in 1991.
In 1991-1993 he worked in the Comparative Planetology laboratory at Vernadsky Institute of Geochemistry (GEOKHI) Russian Academy of Science (RAS), focusing on the evolution of small bodies and dwarf planets   and the transition to a regular shape in the case of massive bodies with critical mass. In 1993-1994 as DAAD (German Academic Exchange) fellowship holder, he studied in the institutes of Physics and Computer Sciences, University of Leipzig, Germany.
Since 2009, he has been at the Carbon Geochemistry laboratory of GEOKHI RAS as a senior researcher. His  work was on multidisciplinary problems related to the evolution of Solar System bodies: planets, small bodies and asteroids to provide constraints on theirs internal structure and properties.

About this English GeoScience Café session
(1) At 19:00, Sep. 23rd, 2018, Professor Voropaev S. A attended English GeoScience Café No.26 and spoke about the topic “Planets and Roche limit distance: Asteroid disruption and meteorites”. The host introduced the speaker. Professor Voropaev S. A started his talk with the background. He then outlined seven parts of his presentation were as follows:
(2) What is Roche Limit Distance?
(3) Examples of Roche limit violations
(4) The Chelyabinsk Meteorite
(5) Introduction to Geochemistry
(6) Vladimir Vernadsky
(7) The Soviet Union’s Moon program
(8) Why do we need to study the Lunar regolith?
Figure. 1 Prof. Voropaev S.A is giving a talk in EGSC session 26

1.    What is Roche Limit Distance?
At the beginning of the lecture, Dr. Leonid Zotov illustrated the equipment for different Satellites.
                     
              
Figure. 2 roche limit distance for fluid satellites and for rigid satellites

2.    Examples of Roche limit violations:
Then Professor Voropaev S. A presented some examples of violations of Roche Limit Distance.
The most famous example is Phobos, a rigid body, which is a small satellite of Mars. Its distance from Mars and its density (D=9376 Km approx). The distance of Phobos from Mars is within its Roche (Liquid) distance.
 
Figure. 3 Phobos(a small satellite of Mars)
Another Example of a violation is Pan. It is one of the satellites of Saturn. Here, a violation here, as its distance from Saturn is within the Roche limit distance.
 
Figure. 4 Pan(one of the satellites of Saturn)
There is a very interesting example of Tidal disruption of Comet Shoemaker Levy-9 comet by planet Jupiter in 1992. It was disintegrated into 21 pieces and after orbiting Jupiter for two years, it entered the planet’s atmosphere. Here the constant factor of Roche is 1.05, which is much smaller than the Roche Rigid distance. It shows that this disintegration also depends on some other factors as well, such as tensile compressive strength of the satellite.
 
Figure. 5 Comet Shoemaker Levy-9
 
3.    Chelyabinsk Meteorite:
After discussing some examples, Voropaev introduced some information about types, sampling of Chelyabinsk (Russia) meteorite that fell to Earth on the 15th of February, 2013. We know the Chondrule was about 1.2 million years old(Fig. 6) and the Chondrule after impact(Fig. 7).

                                   
Figure. 6 Chondrule           
 
Figure. 7 Chondrule after Impact
Voropaev discussed some samples taken out of the whole block (Fig. 8) a 3 axial loading engine compressed them into cylindrical shapes. On compression, the stress to strain relation of the ordinary chondrite (a) and impact melt (b) was demonstrated.
 
Figure. 8 Cylindrical Samples for Compression Analysis

 
Fig.9 exhibits that the ordinary chondrite (A) behaves linear as pressure was applied, but in case of the Impact melt (B) some deformation recurred as the pressure increases from 3 MPa.

(A) Ordinary Chondrite                  (B) Impact melt
Figure. 9 Stress to Strain
 
4.    Introduction to Geochemistry:
Professor Voropaev S. A talked about Geochemistry, and the means for calculating the meteorological age of the layers of the earth. He also discussed the Earth’s place in the meteorological age table. Geochemistry determines the element classification based on this table.
Professor Voropaev S. A gave some examples, like a satellite of Jupiter, Io, with very active volcanos.. There was a very fresh volcano event on it, which means Io has very active volcanoes. It was about seven years between the Galileo mission and the New Horizon mission.
Europa is a satellite with an ice shell. Under this ice shell, there is water, and some cracks-huge cracks on the surface. Europa is most amazing and exciting target, and the next NASA mission in 2022 is going to orbit Europa to explore its ice shell using a dipping mechanism and with some small submarines.
 
Figure. 10 Internal composition of earth and moon
 
5.    Vladimir Vernadsky:
Professor Voropaev S. A mentioned Vladimir Vernadsky in his talk, a director and founder of his institute, and one of the founders of geochemistry.  He was the founding father of Russian cosmology as he considered earth as a whole planet as a system of processes where life and geological processes are interrelated and very close to each other, saying that life is a geological force. He also said that there is an evolution at the earth's sphere- the geosphere, the biosphere, and the noosphere. The noosphere is sphere of knowledge, and human ideas. He said that human cognition is planetary phenomenon.

6.    The Soviet Union`s Moon program
Professor Voropaev S. A then introduced some successful Soviet missions to the moon, including Luna-1, Luna-3, Luna-10, AMS-6, Luna-17/Lunokhod-1, Luna-16, Luna-20, Luna-24, Luna-25, Luna-26, and Luna-27.
The Luna-1 spacecraft was launched in January 1959, which was the first satellite to the moon and equipped with magnetometer and meteoroid sensor. It detected a very low magnetic field near the moon.  
 
Figure. 11 Luna-1 Spacecraft
The Luna-3 was launched in October 1959. It was equipped with a camera and mass-spectrometer. The main achievement was to orbit the moon and collecting far-side images.
 
Figure. 12 Luna-3 Spacecraft
The Luna-10 spacecraft launched to the moon in March 1966 included an orbiter and landing station. The mass of landing probe on Luna-10 was around 240 kg. It was equipped with 3-component magnetometer, a thermal emission sensor and y-spectrometer. The main achievement was an analysis of the meteorological composition of the mare and highland.
 
Figure. 13 Luna-10 Spacecraf
The Luna-16 spacecraft was sent to the moon in September 1970. It was successfully landed on the moon and after landing, an arm went down in the surface to collect about 101g of soil from Mare Fecunditatis;it then returned to earth. The lab at GEOKHI RAS analyzed the soil and it is still preserved there.
 
Figure. 14 Luna-16 Spacecraft
The most successful spacecraft of the moon program was Luna-24, and it was sent to the moon on August 1976. It was equipped with extendable arm with advanced drilling mechanism that can deep drill to three meters.
 
Figure. 15 Luna-24 Spacecraft
The next generation of moon spacecraft named Luna-25 and its landing station now is under development by Russia. The landing station of Luna-25 about one ton and it is equipped with the neutron detector, LAND, for ice searches, a Laser mass-spectrometer, a IR spectrometer, and a thermo sensor.
 
Figure. 16 Luna-25 Spacecraft
The next station is the Luna-26 Orbiter, planned to be launched in 2022. The main aim of this mission is remote sensing and to search for ice on moon, essential to future moon base plans.
 
Figure. 17 Luna-26 Spacecraft
Another landing station named Luna 27 will be launched in 2023. The mass of this landing station is about three tons. It has a Neutron detector, Laser mass-spectrometer, IR spectrometer, Seismometer and 1 m of drilling capability. It is also capable of in-situ sample analysis.
 
Figure. 18 Luna 27 Spacecraft
 
7.    Why do we need to study Lunar regolith?
It was estimated that the lunar regolith is about six meters. These six meters records billions of years of Solar System history. Each layer contains approximately 100 million years of that history, enabling scientists to study the evolution and processes. Studying lunar regolith could lead to many scientific breakthroughs. The impact craters on moon and the layers of the regolith may provide great information, especially about elements like water, oxygen, metals and noble gases. All this knowledge, from practical point of view, will be very useful for future lunar bases.
Considering the aforementioned need, there was a great development in the Drilling mechanism. Fig. 19 demonstrates a drilling tube. Its drilling capability was about 20 m to the bottom of Lunar regolith. With this, scientists could measure density, strength, magnetic property electricity layer by layer.
 
Figure. 19 Drilling Mechanism
Professor Voropaev S. A ended his talk on a next-generation lunar probe, and“robot-geology. It has an extendable drilling mechanism and is currently under development.
 
Figure. 20 Robot-geolog

Q & A
Questioner: Chelyabinsk (meteorite) is a part of a family. Do you think there would be a continuation?
Prof Voropaev: Yes, you are right. It is a very good question. So, there are huge impacts happening in the main asteroid belt and these impacts will be a reason to explore these near earth objects of Apollo and Amor family of asteroids. These families are located near earth and sometimes a huge meteorite comes near earth’s orbit. Chelyabinsk is a member of Apollo family. The Apollo family was created 300 million years ago.  



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