possible on satellite missions simply because the technology is newer. But that
was not always the case.
We forget that over a century years ago, Austrian physicist Victor Francis Hess
undertook the study that, for many years, had puzzled scientists about the levels of
ionizing radiation present in the atmosphere. The assumption at the time was that
the radiation originated from the Earth, and that it would decrease with the distance above ground. Previously, instruments indicated that at higher altitudes in
the atmosphere this radiation might actually be more intense than seen on the
ground. Hess approached this mystery first by greatly increasing the precision of
the measuring equipment and then he personally took it aloft using a balloon. He
systematically measured the radiation at altitudes up to 5.3 km (17,384 ft) with a
number of flights during the period 1911-1913. Those were daring flights for the
time. They were made both during the day and night, and at significant personal
risk. His meticulous work showed that the level of radiation decreased up to an
altitude of about 1 km (3,280 ft) but above that the level increased considerably,
with the radiation detected at 5 km (16,400 ft) being about twice that at sea level.
He concluded that the radiation penetrated the atmosphere from outer space. His
discovery was confirmed by Robert Andrews Millikan in 1925, who coined the
name “cosmic rays” for this radiation. Hess’ discovery opened the door to many
new discoveries in particle and nuclear physics. In particular, both the positron (an
electron with a positive electric charge) and the muon (a heavy form of the electron) were first noticed in cosmic ray experiments by Carl David Anderson. Hess
and Anderson shared the 1936 Nobel Prize in Physics.
This discovery is the basis for many of the balloon flights from Australia and
Antarctic today. Over the past decades, evidence accumulated from detectors on
NASA’s satellites and balloon-borne instruments has allowed scientists to work
out a general picture of cosmic ray sources. Approximately 20% of cosmic rays
were thought to arise from massive stars and supernova debris, with 80% from
interstellar dust and gas with chemical quantities similar to that which exists in the
solar system.
Neutron stars, the crushed cores of massive stars that exploded as supernovas
are the densest objects scientists can study directly. A system in which two neutron stars orbit each other emits gravitational waves, which are ripples in spacetime predicted by Einstein’s General Theory of Relativity. The waves remove
orbital energy, causing the stars to draw ever closer until they eventually crash
together and merge. Some balloon scientists are still studying the theory that it’s
possible that neutron star mergers are the dominant source of heavy, neutron-rich
cosmic rays. Past, recent and future balloon missions are designed to determine if
some, or all of the very neutron-rich elements heavier than iron, might be produced by neutron star mergers rather than in supernovas. Think about that when
next you look at your wedding ring and your wife’s jewelry.
Conclusions 251
was not always the case.
We forget that over a century years ago, Austrian physicist Victor Francis Hess
undertook the study that, for many years, had puzzled scientists about the levels of
ionizing radiation present in the atmosphere. The assumption at the time was that
the radiation originated from the Earth, and that it would decrease with the distance above ground. Previously, instruments indicated that at higher altitudes in
the atmosphere this radiation might actually be more intense than seen on the
ground. Hess approached this mystery first by greatly increasing the precision of
the measuring equipment and then he personally took it aloft using a balloon. He
systematically measured the radiation at altitudes up to 5.3 km (17,384 ft) with a
number of flights during the period 1911-1913. Those were daring flights for the
time. They were made both during the day and night, and at significant personal
risk. His meticulous work showed that the level of radiation decreased up to an
altitude of about 1 km (3,280 ft) but above that the level increased considerably,
with the radiation detected at 5 km (16,400 ft) being about twice that at sea level.
He concluded that the radiation penetrated the atmosphere from outer space. His
discovery was confirmed by Robert Andrews Millikan in 1925, who coined the
name “cosmic rays” for this radiation. Hess’ discovery opened the door to many
new discoveries in particle and nuclear physics. In particular, both the positron (an
electron with a positive electric charge) and the muon (a heavy form of the electron) were first noticed in cosmic ray experiments by Carl David Anderson. Hess
and Anderson shared the 1936 Nobel Prize in Physics.
This discovery is the basis for many of the balloon flights from Australia and
Antarctic today. Over the past decades, evidence accumulated from detectors on
NASA’s satellites and balloon-borne instruments has allowed scientists to work
out a general picture of cosmic ray sources. Approximately 20% of cosmic rays
were thought to arise from massive stars and supernova debris, with 80% from
interstellar dust and gas with chemical quantities similar to that which exists in the
solar system.
Neutron stars, the crushed cores of massive stars that exploded as supernovas
are the densest objects scientists can study directly. A system in which two neutron stars orbit each other emits gravitational waves, which are ripples in spacetime predicted by Einstein’s General Theory of Relativity. The waves remove
orbital energy, causing the stars to draw ever closer until they eventually crash
together and merge. Some balloon scientists are still studying the theory that it’s
possible that neutron star mergers are the dominant source of heavy, neutron-rich
cosmic rays. Past, recent and future balloon missions are designed to determine if
some, or all of the very neutron-rich elements heavier than iron, might be produced by neutron star mergers rather than in supernovas. Think about that when
next you look at your wedding ring and your wife’s jewelry.
Conclusions 251