Tom Krimigis, the man behind the Missions

Europlanet Interview: Stamatios (Tom) Krimigis

Tom Krimigis is a space scientist, of Greek origin, who has been heavily involved in most robotic missions for space exploration to almost every planet in our solar system.

Dr Krimigis is one of the very few scientists that have been invited to meet and brief world leaders about scientific achievements. These include President Reagan in 1986, President Gorbachev in 1987, and President Bush in 1990. He has often testified before Congressional Committees on issues of Space Science and Technology and has participated in many advisory committees for the US Government. Dr Krimigis has also been instrumental in setting up NASA's Discovery program for low-cost planetary missions. Eleven Discovery missions have been chosen so far, the most high profile one being NEAR, the first mission to orbit and land on an asteroid (Eros).

Dr Krimigis' research interests encompass a large variety of topics, including the Sun, the magnetospheres of the Earth and other planets, and the interplanetary medium. He has published more than 380 articles in scientific journals and books and he is one of the most cited scientists in his field.  He has delivered more than 1000 talks and lectures all over the world. In parallel with his scientific achievements he has been actively involved in science outreach through several public talks and is currently serving as the Chair of the Strategic Advisory Board of Europlanet-RI.

Dr Krimigis has played a leading role in several NASA - ESA missions, including Principal Investigator on the Low Energy Charged Particle (LECP) experiments carried by Voyager 1 and 2. More than 30 years after their launch in 1977, the spacecrafts are fast approaching the heliopause, the boundary that separates the solar plasma from the interstellar medium. Voyager 1 crossed the termination shock of the solar wind, at 94 Astronomical Units (AU), on December 2004 and Voyager 2 crossed the termination shock, at 83.65 AU, on August 2007.  At this point the two spacecrafts are in opposite directions, at the Solar System boundaries. The LECP instruments continue to monitor the solar plasma and to measure the energetic particle activity in the outer heliosphere, at the heliopause and in the future in the interstellar plasma, providing scientists with invaluable data for several decades now.

Dr Krimigis is PI of the Cassini spacecraft's Magnetospheric Imaging Instrument (MIMI). Recently, Dr Krimigis and collaborators have published results from Cassini in the leading journal Science that challenge the conventional view of the shape of the heliosphere.


An Interview

Dr. Eleni Chatzichristou (EC) talked to Dr. Tom Krimigis (TK) about his achievements and inspirations:

EC: What does the new discovery (on the shape of the heliosphere) mean for our understanding of the solar system?

TK: The images from the Cassini/MIMI/INCA instrument have revolutionized what we thought we knew for the past fifty years; the solar system travels through the local interstellar medium not like a comet but more like a big, round bubble. More specifically, models had predicted a foreshortened "nose" in the direction of the solar system's motion, and an elongated "tail" in the opposite direction. The map we've created from INCA's images suggests that pressure from a hot population of charged particles and interaction with the interstellar medium's magnetic field strongly influence the shape of the heliosphere, and shape it into a "bubble". 

EC: What are your plans for the next decade and what would be the next step(s) for NASA/ESA in planetary missions?

TK: My own plans for the next decade are to follow the data from our instruments on Voyagers 1 and 2, now in the heliosheath at 114 and ~90 AU, respectively, and find out where the heliopause, the true boundary with the interstellar medium, is located. Also, to analyze data from our instrument on Cassini and see the progress and eventual end of the Cassini Solstice Mission, scheduled to conclude in 2017. And before that, to see the New Horizons encounter with Pluto in July 2015. The planetary program has some very exciting missions in the planning stages, such as the EJSM (Europa Jupiter System Mission), and eventually TandEM (Titan and Enceladus Mission). The origin of possible biological activity looms large as a science goal, among several others. Future research can't get much better than that!

EC: Is there a competition or primarily collaboration between ESA and NASA, and where do you think ESA lags behind the American agency? 

TK: I don't believe there is competition, but rather complementarity. For example, neither agency could afford EJSM or TandEM alone. Both are joint endeavors and coordinated well between ESA and NASA. Of course, NASA can have a more extensive program, since it has nearly three times the budget that ESA has.

EC: You have created your successful career all by yourself at a time when the space programs were just starting and you found yourself right in the middle of where things were happening. How easy do you think is for young talented space scientists to become equally successful today?

TK: Sometimes one can be at the right place at the right time-I was lucky enough to get to the University of Iowa only a few years after Van Allen discovered the radiation belts (Van Allen Belts). It was a very exciting time, with new discoveries coming one right after another. That's when I built my first instrument for a planetary mission, the Mariner 4 spacecraft to Mars, then another one to Venus, with Mariner 5. After that followed Voyager (by now at Johns Hopkins Applied Physics Lab), and Gallileo, and Ulysses and Cassini, MESSENGER, and New Horizons. It's a wonderful feeling, to have built instruments that have gone to all the planets. Needless-to-say, it's more difficult for a young scientist today-all the "low-hanging fruit' has been picked. But there are still plenty of opportunities for younger scientists for discoveries that could change our views on rather fundamental issues. A key example is the quest for biological activity, current or past, on solar system bodies; it has been a long-term objective and has not been answered by my generation of scientists- and there are many others!

EC: What is the major challenge in space exploration and what has been the major challenge(s) for you in your career?

TK: I'm not sure I know them all-but the search for life's origins is clearly the top.

As for me, the major challenge has always been the degree of risk one should take in designing instruments (and spacecraft). I faced that early on, when I used very thin (25 micron) totally depleted solid state detectors to search (successfully) for He and CNO in the Van Allen Belts (on Injun 4, in 1964). None knew at the time whether these would survive in space, nor their radiation susceptibility. Then I took a risk in flying a stepper motor to rotate the detector heads on the Voyager missions-the only way to obtain angular distribution information. I was told it would fail in six months, but both motors are still stepping every 192 seconds after nearly 33 years. Without stepping, we would have missed out on key discoveries at all the outer planets as well as the heliospheric termination shock.

EC: After so many years of an active successful career what is the major lesson that you have learned from life?

TK: I learned that major discoveries entail taking big (experimental) risks. Taking incremental steps rarely pays off, and it's very boring to boot!

Early years

Dr Tom Krimigis was born in the Greek island of Chios, where he spent his school years. He then moved to the University of Minnesota (USA) where he obtained his Bachelors’ degree in 1961, followed by a Masters’ in 1963 from the University of Iowa. He then became a student of J.A. van Allen, with whom he has published some of his best known works, such as the first use of a solid detector in space and the discovery of alpha particles (helium) in the radiation belts. Dr Krimigis obtained his PhD in 1965 from the University of Iowa where he was immediately employed as a faculty of the Physics and Astronomy Dept., before joining the Johns Hopkins University Applied Physics Laboratory (APL) three years later. He later headed the Space Physics and Instrumentation Group, became Chief Scientist in 1980, Head of the Space Department in 1991 until 2004, and Emeritus Head since then. The APL Space Department’s work concerns the design, construction and launching of scientific instruments, as well as of entire satellites, for space missions.

The Man Behind the Missions

Tom Krimigis has been Principal Investigator and Co-Investigator in several NASA - ESA missions: Among them are the Low Energy Charged Particle Experiment on Voyagers 1 and 2 (Jupiter, Saturn and beyond), the Mariner 3,4 (Mars) and 5 (Venus) missions, the Active Magnetospheric Particle Tracer Explorer (first man-made "comet" in space), the extremely successful Cassini-Huygens mission to Saturn and Titan. He was equally involved with other famous missions studying objects of our solar system, such as Galileo (Jupiter), Ulysses (Sun), ACE (interplanetary medium), MESSENGER (Mercury), and New Horizons (Pluto).

For his achievements he has received some twenty NASA Group Achievement Awards. He was furthermore awarded twice (in 1981 and 1986) the NASA Medal for Exceptional Scientific Achievement, the International Academy of Astronautics Basic Sciences Award and the AHEPA Academy Prize, both in 1994. In 1977 the Greek President has awarded him with the Gold Cross "Commandeur de ‘Ordre du Phoenix" and in 1998 the American Hellenic Institute has honored him with the "Hellenic Heritage Achievement Award". In 1999 the International Astronomical Union named an asteroid as "8323 Krimigis", in his honor. Since 2004 he is an elected member of the Athens Academy.



Left: The traditional paradigm of what the solar system looks like as it travels through the interstellar medium (W.I. Axford, Space. Sci. Rev. 14,582, 1973). Right: The new Cassini results indicate a very different picture for the heliosphere (T. Krimigis et al., Science 326,971, 2009). Images and animations at the European Geosciences Union (EGU) press conference webcast.



Astronomical Unit (AU): 1 Astronomical Unit is the average distance between the Earth and the Sun, approximately equal to 150 million kilometers (149,598,000 km).

Heliosphere: The bubble in space around our solar system which is filled with the energetic particles and ions of the solar wind and its associated magnetic field (solar magnetosphere). The heliosphere extends out to about 100 AU (1 Astronomical Unit is the average distance between the Sun and the Earth, equal to 150 million kilometers)  The heliosphere's boundary is considered to be the point where the interstellar medium counterbalances the solar wind pressure, and it is called the heliopause.

Interstellar Medium:The space between the stars of a galaxy, filled (even though very dilute) with gas, dust and cosmic rays. The interstellar medium gets enriched in heavier elements through stellar explosions during the stars lifecycle, and then recycles this matter through the formation of new stars in its densest regions. 

Magnetosphere:All planets with intrinsic magnetic field (including the Earth) deflect the solar wind, creating around them a magnetosphere consisting of ions and electrons which come from the solar wind and the planet's ionosphere.

Radiation Belts: The Earth has two regions of trapped fast particles: The inner radiation belt, discovered by van Allen, extends about one Earth radius (6731 km) above the equator and consists of very energetic protons produced by the interaction of cosmic rays with atoms of the Earth's atmosphere. The outer radiation belt consists of ions and electrons of lower energy and is directly influenced by the magnetic storms (disturbances of the Earth's magnetosphere, related to space weather phenomena). The outer radiation belt contains also alpha particles, that is, atoms of helium which have lost their two electrons and are mainly found in the solar wind.

Solar Plasma:The solar plasma consists from protons and electrons primarily. It also contains ions of helium and heavier elements and it trains solar magnetic field lines with it as it escapes from the Sun.

Solid State Detector: The most recent class of detector developed is the solid state detector. These detectors convert the incident photons of ionizing radiation directly into electrical pulses/signal. Solid state detectors are made from a variety of semi-conducting materials, depending on the application we intend to use them for, including: germanium, silicon, cadmium telluride, mercuric iodide, and cadmium zinc telluride.The charge collected is proportional to the energy deposited in the detector and therefore these devices can also yield information about the energy of individual particles or photons of radiation.

Termination Shock:When the solar wind leaves the sun, and for several billion kilometers further in the heliosphere, it travels at very high speed (up to 800 km/sec). Further out, when it starts colliding with the interstellar medium, it slows down and becomes subsonic. The area in space where this happens is called the termination shock.