If life exists elsewhere in our solar system, it may not have developed independently from life on Earth. Instead, it’s possible that microbes from Earth may have colonized other planets or moons by hitching a ride on a rock blasted from Earth’s surface by a meteor impact. If the impact gives the rock enough energy to escape into space (while at the same time not raising its temperature so high as to “cook” the microbes), the rock may eventually reach another body in the solar system. In fact, rocks from Mars are known to have reached Earth in just this way, although none are currently known to have contained microbes. Computer modeling can be used to estimate the probability that a rock ejected from the surface of the Earth with a speed greater than the escape speed will reach another planet. These computer models indicate that under the influence of gravitational fields from the other objects in the solar system, an ejected rock can take millions of years to travel from one planet to another. During this time any life “aboard” is continually exposed to the high radiation levels of space. Some researchers have calculated that a 3.0-m-diameter rock at a typical rock density of 3.0 g/cm 3 is sufficient to shield some types of microbes from the hostile environment of space for several million years of travel. The accompanying plot shows the residual speed of an ejected object—that is, the speed the object would have when infinitely far from the Earth—as a function of its speed at the surface of the Earth (its original ejection speed). By simulating the motion of rocks ejected from the Earth with a variety of speeds, researchers conclude that 0.03% of the rocks ejected such that they have a residual speed of 2.5 km/s will have reached Mars 2.0 million years later. Although this doesn’t seem like a high probability, there have been so many meteor impacts over the long history of the Earth that many ejected rocks must have reached Mars—though whether they carried microbes, and if they did, whether the microbes would have survived, are open questions. 91. • What is the minimum kinetic energy an impact must give to a 3.0-m-diameter rock for the rock to be able to escape from the Earth? A. 5.3 × 10 3 J B. 1.3 × 10 6 J C. 2.7 × 10 12 J D. 2.1 × 10 13 J
If life exists elsewhere in our solar system, it may not have developed independently from life on Earth. Instead, it’s possible that microbes from Earth may have colonized other planets or moons by hitching a ride on a rock blasted from Earth’s surface by a meteor impact. If the impact gives the rock enough energy to escape into space (while at the same time not raising its temperature so high as to “cook” the microbes), the rock may eventually reach another body in the solar system. In fact, rocks from Mars are known to have reached Earth in just this way, although none are currently known to have contained microbes. Computer modeling can be used to estimate the probability that a rock ejected from the surface of the Earth with a speed greater than the escape speed will reach another planet. These computer models indicate that under the influence of gravitational fields from the other objects in the solar system, an ejected rock can take millions of years to travel from one planet to another. During this time any life “aboard” is continually exposed to the high radiation levels of space. Some researchers have calculated that a 3.0-m-diameter rock at a typical rock density of 3.0 g/cm 3 is sufficient to shield some types of microbes from the hostile environment of space for several million years of travel. The accompanying plot shows the residual speed of an ejected object—that is, the speed the object would have when infinitely far from the Earth—as a function of its speed at the surface of the Earth (its original ejection speed). By simulating the motion of rocks ejected from the Earth with a variety of speeds, researchers conclude that 0.03% of the rocks ejected such that they have a residual speed of 2.5 km/s will have reached Mars 2.0 million years later. Although this doesn’t seem like a high probability, there have been so many meteor impacts over the long history of the Earth that many ejected rocks must have reached Mars—though whether they carried microbes, and if they did, whether the microbes would have survived, are open questions. 91. • What is the minimum kinetic energy an impact must give to a 3.0-m-diameter rock for the rock to be able to escape from the Earth? A. 5.3 × 10 3 J B. 1.3 × 10 6 J C. 2.7 × 10 12 J D. 2.1 × 10 13 J
If life exists elsewhere in our solar system, it may not have developed independently from life on Earth. Instead, it’s possible that microbes from Earth may have colonized other planets or moons by hitching a ride on a rock blasted from Earth’s surface by a meteor impact. If the impact gives the rock enough energy to escape into space (while at the same time not raising its temperature so high as to “cook” the microbes), the rock may eventually reach another body in the solar system. In fact, rocks from Mars are known to have reached Earth in just this way, although none are currently known to have contained microbes. Computer modeling can be used to estimate the probability that a rock ejected from the surface of the Earth with a speed greater than the escape speed will reach another planet. These computer models indicate that under the influence of gravitational fields from the other objects in the solar system, an ejected rock can take millions of years to travel from one planet to another. During this time any life “aboard” is continually exposed to the high radiation levels of space. Some researchers have calculated that a 3.0-m-diameter rock at a typical rock density of 3.0 g/cm3 is sufficient to shield some types of microbes from the hostile environment of space for several million years of travel.
The accompanying plot shows the residual speed of an ejected object—that is, the speed the object would have when infinitely far from the Earth—as a function of its speed at the surface of the Earth (its original ejection speed). By simulating the motion of rocks ejected from the Earth with a variety of speeds, researchers conclude that 0.03% of the rocks ejected such that they have a residual speed of 2.5 km/s will have reached Mars 2.0 million years later. Although this doesn’t seem like a high probability, there have been so many meteor impacts over the long history of the Earth that many ejected rocks must have reached Mars—though whether they carried microbes, and if they did, whether the microbes would have survived, are open questions.
91. • What is the minimum kinetic energy an impact must give to a 3.0-m-diameter rock for the rock to be able to escape from the Earth?
A radio broadcast left Earth in 1911. How far in light years has it traveled?
If there is, on average, 1 star system per 400 cubic light years, how many star systems has this broadcast reached?
Assume that the fraction of these star systems that have planets is 0.50 and that, in a given planetary system, the average number of planets that have orbited in the habitable zone for 4 billion years is 0.20. How many possible planets with life could have heard this signal?
We think the terrestrial planets formed around solid “seeds” that later grew over time through the accretion of rocks and metals.
a) Suppose the Earth grew to its present size in 1 million years through the accretion of particles averaging 100 grams each. On average, how many particles did the Earth capture per second, given that the mass of the Earth is = 5.972 × 10 ^24 kg ?
b) If you stood on Earth during its formation and watched a region covering 100 m^2, how many impacts would you expect to see in one hour. Use the impact rate you calculated in part a. You’ll need the following as well: the radius of the Earth is = 6.371 × 10 ^6 m and the surface area of the Earth is 4??^2Earth
In a globular cluster, astronomers (someday) discover a star with the same mass as our Sun, but consisting entirely of hydrogen and helium. Is this star a good place to point our SETI antennas and search for radio signals from an advanced civilization?
Group of answer choices
No, because such a star (and any planets around it) would not have the heavier elements (carbon, nitrogen, oxygen, etc.) that we believe are necessary to start life as we know it.
Yes, because globular clusters are among the closest star clusters to us, so that they would be easy to search for radio signals.
Yes, because we have already found radio signals from another civilization living near a star in a globular cluster.
No, because such a star would most likely not have a stable (main-sequence) stage that is long enough for a technological civilization to develop.
Yes, because such a star is probably old and a technological civilization will have had a long time to evolve and develop there.
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