2. The Traveling Exhibit Science Background Part B: Star & Planet Formation prepared by Dr. Cherilynn Morrow for the Space Science Institute Boulder, CO

3. B. Star and Planet Formation KEY QUESTIONS: Where do stars & planets we observe in the galaxy come from? Around which kinds of stars should we look for signs of life?

4. *In 1859, Huggins began observing the stars using Bunsen's and Kirchhoff's discoveries that spectral emission and absorption lines could reveal the composition of the source. We are Star Stuff The Astronomical Spectroscopy of Sir William Huggins One important object of this original spectroscopic investigation * of the light of the stars and other celestial bodies, namely to discover whether the same chemical elements as those of our earth are present throughout the universe, was most satisfactorily settled in the affirmative; a common chemistry, it was shown, exists throughout the universe. - Sir William Huggins Huggins private observatory Tulse Hill, London

5. Artist Concept: Early star-planet system in formation proto-planetary disk Star and Planet Formation Where do stars and planets come from? Planets sometimes form along with a central star out of the same swirling disk of gas and dust. Our search for life beyond our solar system requires knowing where and how this process occurs. The best chance to find an Alien Earth might be to look around stars like our Sun. The birth of star systems where life evolves depends on the death of massive stars that spew out elements like carbon & oxygen.

6. Searching Around Sun-Like Stars Why search for planets and life around Sun-like stars ? We know that in our case, a planet (Earth) with life has evolved around such a star. High-mass stars (> 10 times the mass of the Sun) burn brightly with ultraviolet radiation that tends to destroy proto-planetary disks. Massive stars also have relatively short lifetimes (1 to 10 million years as compared to 10 billion years for the Sun). This is not time enough for planets with life to evolve. Low-mass stars (< 0.6 times the mass of the Sun) are relatively dim and have very long lifetimes: there is time enough for life to evolve around them. Their dimmer light sometimes makes observations more challenging.

7. Stars have life cycles. They are born and they die but are not alive like us. Stars like the Sun die by puffing off their outer layers of gas and dust. This process creates a beautiful variety of NEBULAE in the Milky Way GALAXY. Butterfly Nebula Cat Eye Nebula Eskimo Nebula When Sun-Like Stars Die

8. Blue giant stars that are much more massive than the Sun form elements heavier than hydrogen & helium (e.g. carbon, nitrogen, oxygen) via nuclear fusion in their cores. When Massive Stars Die Crab Nebula: Supernova Remnant Such massive stars die in incredibly powerful explosions called supernovas. Supernovas spew heavier elements needed for life out into the galaxy. The explosions themselves can stimulate new star birth by sending shock waves into nearby clouds of gas & dust. Stars Have Life Cycles

9. Supernova Remnant Another beautiful supernova remnant, just for fun!

10. The Right Stuff Supernovas help ensure that heavier elements and complex molecules are found throughout interstellar space. Since the building blocks of life are so utterly common, perhaps it might not be so strange to find life everywhere! And yet, the living cell is so amazingly complex that we must wonder if it commonly emerges and survives, even on other Earth-like worlds.

11. Forming Worlds Where Life Can Exist Artists concept of the formation of OUR SOLAR SYSTEM 1. Something (perhaps a supernova) triggers the gravitational collapse of a nearby interstellar cloud. The cloud naturally heats up and spins faster as it collapses. Collisions between particles flatten the cloud into a disk. 2. The Sun and planets start to form in this spinning, flattened disk (proto- planetary disk), with the Sun at the hottest central part. 3. In our Solar System, Earth formed in the inner region of the disk where rocky & metallic material could condense in the greater heat. Ices & hydrocarbons settled in the outer regions where gas giants like Jupiter form. 4. Computer models tell us that Jupiters gravity played a strong role in causing comet & asteroid impacts to supply water & organic materials to Earth from the outer solar system, thus contributing to its habitability.

12. These large clouds of gas and dust in our Milky Way galaxy are the types of regions where many stars are forming: Orion and Eagle NEBULAS. Orion Eagle Our entire solar system would fit in this small nub Star Forming Regions

13. HST Images of Proto-planetary Disks Proto-planetary disks around young stars in the Orion Nebula. The disks range in size from 2 to 8 times the diameter of our Solar System.

14. Artist Concept: NASAs Spitzer Spacecraft Spitzer Sees through the Dust Where do stars and planets come from? Spitzer is the largest infrared telescope ever launched into space. Many areas of space are filled with vast, dense clouds of gas and dust which block our view. Infrared (IR) light, can penetrate these clouds, allowing us to peer into regions of star formation and into newly forming planetary systems.

15. Now You See Stars, Now You Don't The image composite compares an infrared image taken by NASA's Spitzer Space Telescope to a visible- light picture of the same region (inset). The added detail in the Spitzer image reveals a dynamic region in the process of evolving and creating new stellar life. Spitzer is both seeing, and seeing through, the dust.

16. A striking comparison, just for fun!

17. There are round heat sources beneath the nebula on the table which cannot be seen with the human eye, but which are being seen by the infrared camera and recorded on the monitor. The IR light shines right through the table! In a similar way, the Spitzer Telescope can detect infrared radiation shining through dusty interstellar clouds revealing young stars in formation. Alien Earths: Infrared (IR) Camera Interactive Overhead Infrared Camera looking down at nebula The monitor displays what the IR camera is seeing Heat source beneath the nebula on the round table Cone Nebula star forming region Yes! I wonder whatll happen if we put our eyeglasses under the IR camera? Our hands look red on the screen. We emit IR light!

18. Alien Earths: Design a Solar System Touch Screen Interactive Based on real, multi-body model simulations of the stability of planetary orbits. Design a Solar System Hey, I can drag a bunch of planets in orbit around a star and then let them zoom around to see if they will fly out of the system, or crash into each other, or be gobbled up by the star! Computer models show that not every configuration of planets is a stable one. The gravitational effect of a Jupiter- sized planet in a close elliptical orbit can be to kick terrestrial planets out of the system. Jupiter-sized worlds in more distant circular orbits are much more helpful to the formation and evolution of Earth- like planets in a habitable zone.

19. Elements heavier than Hydrogen & Helium form inside stars and then are released back into the galaxy when stars die. Thus materials that are the building blocks for life & Earth-like planets are found throughout interstellar space. Planets sometimes form along with a central star out of a common swirling disk of gas and dust. Our search for life beyond our Solar System requires knowing where and how this process occurs. Perhaps the best chance to find an Alien Earth is to look around stars that are most like our Sun. B. Star and Planet Formation SUMMARY