Milestone-Proposal:Discovery of Interstellar Carbon Monoxide
To see comments, or add a comment to this discussion, click here.
Docket #:2024-20
This is a draft proposal, that has not yet been submitted. To submit this proposal, click on the edit button in toolbar above, indicated by an icon displaying a pencil on paper. At the bottom of the form, check the box that says "Submit this proposal to the IEEE History Committee for review. Only check this when the proposal is finished" and save the page.
To the proposer’s knowledge, is this achievement subject to litigation? No
Is the achievement you are proposing more than 25 years old? Yes
Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes
Did the achievement provide a meaningful benefit for humanity? Yes
Was it of at least regional importance? Yes
Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes
Has the IEEE Section(s) in which the plaque(s) will be located agreed to arrange the dedication ceremony? Yes
Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes
Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes
Year or range of years in which the achievement occurred:
1970
Title of the proposed milestone:
Discovery of Interstellar Carbon Monoxide, 1970
Plaque citation summarizing the achievement and its significance; if personal name(s) are included, such name(s) must follow the achievement itself in the citation wording: Text absolutely limited by plaque dimensions to 70 words; 60 is preferable for aesthetic reasons.
On April 4, 1970, using the National Radio Astronomy Observatory (NRAO) 36-foot telescope at Kitt Peak, Arizona USA, Bell Telephone Laboratories scientists Keith B. Jefferts, Arno A. Penzias, and Robert W. Wilson detected interstellar carbon monoxide (CO) at 115 GHz (2.6 mm). This first identification of CO in space enabled tracing of molecular clouds within the Milky Way, revolutionizing radio astronomy, astrochemistry, and the study of star formation. The discovery marked a foundational advance in millimeter-wave spectroscopy of the interstellar medium.
200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.
On April 4, 1970, Bell Telephone Laboratories researchers Keith B. Jefferts, Arno A. Penzias, and Robert W. Wilson made the first detection of interstellar carbon monoxide (CO) using the 36-foot radio telescope at Kitt Peak, Arizona. This landmark achievement opened an entirely new window on the universe. Observing at 115 GHz (2.6 mm wavelength), they identified CO in multiple galactic sources, including Orion A and Sagittarius A, marking the beginning of molecular radio astronomy.
The discovery was transformative. Unlike atomic hydrogen, which traces diffuse interstellar gas, CO became the primary tool for mapping cold, dense molecular clouds — the birthplaces of stars and planets. For the first time, astronomers could systematically chart the structure and dynamics of star-forming regions within the Milky Way and other galaxies. This breakthrough laid the foundation for decades of astronomical surveys and shaped modern understanding of galactic evolution.
Equally significant, this finding ignited the field of astrochemistry. The confirmed presence of molecules in interstellar space spurred a surge of discoveries, revealing a rich and complex molecular universe. Today, over 200 interstellar molecules are known, many playing roles in prebiotic chemistry.
The detection of interstellar CO stands among Bell Labs’ most influential scientific achievements, following its 20 May 1964 discovery of the cosmic microwave background. It showcased the power of radio astronomy and interdisciplinary research in advancing human knowledge. The legacy of this milestone endures in both science and technology, reflected in the instruments, observatories, and discoveries it inspired.
IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.
Communications Society (ComSoc); Microwave Theory and Techniques Society (MTT-S); Antennas and Propagation Society (AP-S); Instrumentation and Measurements (IMS); Photonics; IEEE Aerospace and Electronic Systems Society (AESS); Signal Processing (SP); Education Society (ED); Society on the Social Implications of Technology (SSIT); Geoscience and Remote Sensing Society (GRSS).
In what IEEE section(s) does it reside?
North Jersey Section
IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:
IEEE Organizational Unit(s) paying for milestone plaque(s):
IEEE Organizational Unit(s) arranging the dedication ceremony:
IEEE section(s) monitoring the plaque(s):
IEEE Section: North Jersey Section
IEEE Section Chair name: Hong Zhao, PhD
Milestone proposer(s):
Proposer name: Theodore Sizer II, PhD
Proposer email: Proposer's email masked to public
Proposer name: Gregory Wright, PhD
Proposer email: Proposer's email masked to public
Proposer name: Giovanni Vannucci, PhD
Proposer email: Proposer's email masked to public
Proposer name: Thomas M Willis III, PhD
Proposer email: Proposer's email masked to public
Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.
Street address(es) and GPS coordinates in decimal form of the intended milestone plaque site(s):
Nokia Bell Labs, Bldg. 6, 600 Mountain Ave, Murray Hill, NJ 07974 US (40.684042, -74.400856)
Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.
Please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. Nokia Bell Labs headquarters. There are other historic markers at the site.
Are the original buildings extant?
Yes.
Details of the plaque mounting:
The plaque will be mounted on a stone or plinth on the grounds near the building entrance.
How is the site protected/secured, and in what ways is it accessible to the public?
Who is the present owner of the site(s)?
Nokia Bell Labs.
What is the historical significance of the work (its technological, scientific, or social importance)? If personal names are included in citation, include detailed support at the end of this section preceded by "Justification for Inclusion of Name(s)". (see section 6 of Milestone Guidelines)
Using a National Radio Astronomy Observatory 36-foot telescope in Tuscon, Arizona, Bell Labs Researchers R. W. Wilson, K. B. Jefferts, and A. A. Penzias made the first discovery of the bright radio signal of interstellar carbon monoxide in the Orion Nebula, using a millimeter-wave receiver to detect the molecule's strong emission lines even through dense clouds of interstellar gas. The new methods uncovered details of atoms and molecules, the chemistry of the Milky Way. It revealed details about space at great distances previously not directly observable with telescopes and or obscured by clouds, ushering in a rapid advancement in the field of modern astronomy, in the study of interstellar chemistry, star, and planetary origins.
Millimeter-Wave Spectroscopy: The detection used heterodyne receivers tuned to 115 GHz, pushing the limits of sensitivity and spectral resolution available at the time. The CO lines exhibited characteristic linewidths and radial velocities corresponding to known galactic sources.
Observational Technique: The team employed the 36-foot NRAO telescope at Kitt Peak, one of the few instruments then capable of such observations. The success required precise calibration to distinguish weak spectral lines from instrumental and atmospheric effects.
Significance of Observations:
In Orion A, the CO emission exhibited a linewidth of 5 km/s and an antenna temperature of 39 K — strong evidence of dense molecular gas.
In Sagittarius A, CO emission extended over a 100 km/s velocity range, highlighting the complex dynamics of the galactic center.
Interdisciplinary Impact: This milestone launched the field of millimeter-wave molecular line astronomy, directly influencing radio astronomy, astrophysics, and astrochemistry. It set the stage for large-scale molecular surveys of the Milky Way and external galaxies.
What obstacles (technical, political, geographic) needed to be overcome?
Technical: Observing at 115 GHz required overcoming challenges related to atmospheric absorption, cryogenic receiver design, and noise suppression. The Bell Labs scientists had developed new equipment collaborating with others back in New Jersey, and they brought it to Kitt Peak. Then the Bell Labs scientists made needed repairs and adjustments to the equipment at the NRAO site. Weather conditions cooperated and a measurement was taken right away. The collaboration of the Bell Labs scientists with NRAO provided access to instrumentation capable of millimeter-wave detection.
Scientific Paradigm Shift: The prevailing assumption was that interstellar space lacked sufficient molecules for detection at these wavelengths. The Bell Labs team's success overturned this belief, opening new research frontiers.
What features set this work apart from similar achievements?
Prior to 1970, astronomers had detected only a few interstellar molecules, and the cold, dense molecular clouds believed to be birthplaces of stars remained poorly understood. The detection of interstellar carbon monoxide — the second most abundant molecule in space after molecular hydrogen (H₂) — provided a critical tool for probing these regions.
Bell Labs scientists Keith B. Jefferts, Arno A. Penzias, and Robert W. Wilson hypothesized that CO’s strong dipole moment and abundance could make it detectable at millimeter wavelengths. Collaborating with the National Radio Astronomy Observatory, they conducted observations with NRAO’s 36-foot radio telescope at Kitt Peak, optimized for millimeter-wave research.
On April 4, 1970, they detected the rotational transition of CO (J=1→0) at 115 GHz in emission from multiple galactic sources, including Orion A (Ori A), Sagittarius A (Sgr A), Sagittarius B2 (Sgr B2), W39, and W51. This discovery was first reported in IAU Circular No. 2231, issued by the Central Bureau for Astronomical Telegrams.
The measured spectra showed strong emission lines, confirming CO's presence in widespread molecular clouds. This enabled astronomers to trace molecular gas distributions, study star-forming regions, and develop a detailed understanding of galactic structure.
Why was the achievement successful and impactful?
The 1970 detection of interstellar carbon monoxide (CO) profoundly transformed multiple scientific fields and continues to influence research worldwide.
Radio Astronomy and Astrophysics: The discovery of CO at 115 GHz established molecular spectroscopy as a fundamental tool in radio astronomy. CO became the primary tracer for mapping molecular hydrogen (H₂) — the most abundant molecule in the universe but difficult to detect directly. This enabled astronomers to chart the distribution of molecular clouds across the Milky Way and other galaxies, revealing the large-scale structure, kinematics, and star-forming regions of the galactic disk and spiral arms. Long-term, CO surveys provided essential data for models of galactic dynamics, star formation rates, interstellar medium (ISM) processes, and galaxy evolution. Major projects, such as the Galactic Ring Survey and extragalactic CO surveys, trace their methods directly to this discovery.
Astrochemistry and Molecular Astrophysics: The detection of CO proved that molecules could exist in cold, dense regions of interstellar space, catalyzing a new era in interstellar chemistry research. This discovery encouraged the search for other molecules, leading to the identification of over 200 interstellar species — including organic and prebiotic molecules — and advancing understanding of chemical pathways, molecular cloud physics, and the origin of complex organic compounds in space. The field of astrochemistry, which today spans astrophysics, chemistry, and planetary science, directly grew from this foundational work.
Scientific Instrumentation and Technology: The success of the 1970 detection accelerated advancements in millimeter and submillimeter-wave astronomy, including improvements in cryogenic receivers, heterodyne detection, and large-aperture radio telescopes. It laid groundwork for major observatories like ALMA (Atacama Large Millimeter/submillimeter Array) and key space missions observing molecular lines.
Bell Labs’ Scientific Legacy: The interstellar CO detection cemented Bell Labs' role as a leader in fundamental scientific discovery, following its landmark detection of the Cosmic Microwave Background (CMB) in 1964 by Penzias and Wilson. It demonstrated the ability of an industrial research laboratory to make lasting contributions to both pure science and applied technology, inspiring interdisciplinary collaboration between physics, chemistry, and astronomy.
Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.
Wilson, R. W., K. B. Jefferts, and A. A. Penzias. “Carbon monoxide in the Orion nebula.” The Astrophysical Journal 161 (1970): L43.
IAU Circular No. 2231 (April 1970): Announcement of Discovery of Interstellar Carbon Monoxide by Jefferts, Penzias, and Wilson.
Jefferts, K.B., Penzias, A.A., & Wilson, R.W. (1970). Detection of Carbon Monoxide in the Interstellar Medium. Astrophysical Journal Letters, 161, L85.
Wilson, R.W., Jefferts, K.B., & Penzias, A.A. (1970). Carbon Monoxide in the Galaxy. Astrophysical Journal, 161, L43.
NRAO Historical Archives on the 36-foot Telescope Observations.
Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC): All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to ieee-history@ieee.org. Please see the Milestone Program Guidelines for more information.
Please email a jpeg or PDF a letter in English, or with English translation, from the site owner(s) giving permission to place IEEE milestone plaque on the property, and a letter (or forwarded email) from the appropriate Section Chair supporting the Milestone application to ieee-history@ieee.org with the subject line "Attention: Milestone Administrator." Note that there are multiple texts of the letter depending on whether an IEEE organizational unit other than the section will be paying for the plaque(s).
Please recommend reviewers by emailing their names and email addresses to ieee-history@ieee.org. Please include the docket number and brief title of your proposal in the subject line of all emails.
