[Baps] Gerhard Wurm seminar, Thurs Mar 23, 1pm

[Sarah Stewart-Mukhopadhyay]

Harvard Department of Astronomy
Special Seminar

Planet Formation in Astronomy, Experimental Physics, and Planetary Science:
>From Current Concepts to New Ideas and Further

Dr. Gerhard Wurm
U. Munster, Germany

Thursday, March 23
1:00 PM
Phillips Auditorium
60 Garden St.

  Abstract:  Throughout the history of the Solar System, collisions have
  been an important, inevitable, vital and sometimes destructive part of
  it. In the standard model of planet formation, terrestrial planets and
  their  precursor  planetesimals  are  supposed  to  be  built  through
  sticking collisions. Easy enough, many assume that this sticking works
  whatsoever. Equally well justified, others exclaim it is impossible to
  do  if  particles collide at tens of m/s. So, who is right? Our recent
  impact  experiments  show that "high-speed" collisions between cm-size
  particles  can  lead  to  growth  and - quite non-intuitively at first
  sight  -  might  even  promote  growth  better  than  slow collisions.
  However, this is only one part of the story and it has to be placed in
  the   timeframe   and   location   of   protoplanetary  disks.  Recent
  observations  especially  by the Spitzer telescope give clear evidence
  for  a  very  different  evolution  of  gas and dust in protoplanetary
  disks.  Large  inner  holes  filled  with  gas  but devoid of dust are
  observed  at  transitional  stages.  And  it  is only recently that we
  realized  that  this  might  be  one  of  the most important phases in
  planetary formation.

  Long  known,  but  completely forgotten in astrophysics, a force named
  photophoresis  rules  in  these  environments.  In  an elegant fashion
  already  its  simplest  application  provides  means  to  explain  the
  clearing  of  the  inner disk from dust, to explain circumstellar dust
  rings, to explain the formation of comets and Kuiper belt objects, and
  to  explain  the  formation  of  primitive asteroids and some of their
  descendent  chondritic  meteorites.  New  experiment  on photophoresis
  result   in   still   more   interesting  effects  which,  applied  to
  protoplanetary  disks,  might prevent the loss of solid matter (m-size
  bodies)  to the star. Terrestrial but also giant planet formation will
  not  go  unimpressed  by  this.  And  if  this  were  not  yet enough,
  photophoresis  has  other  applications e.g. on the surface and in the
  atmosphere  of  the current Mars (and Earth) which are so obvious that
  it will easily fit within this talk without restraint.
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